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1.
Colloids Surf B Biointerfaces ; 236: 113832, 2024 Apr.
Article in English | MEDLINE | ID: mdl-38447447

ABSTRACT

The petal effect is identified as a non-wetting state with high drop adhesion. The wetting behavior of petal surfaces is attributed to the papillose structure of their epidermis, which leads to a Cassie-Baxter regime combined with strong pinning sites. Under this scenario, sessile drops are pearl shaped and, unlike lotus-like surfaces, firmly attached to the surface. Petal surfaces are used as inspiration for the fabrication of functional parahydrophobic surfaces such as antibacterial or water-harvesting surfaces. In this work, two types of rose petals were replicated by using a templating technique based in Polydimethylsiloxane (PDMS) nanocasting. The topographic structure, the condensation mechanism under saturated environments and the wetting properties of the natural rose petal and their negative and positive replicas were analyzed. Finally, we performed prospective ice adhesion studies to elucidate whether petal-like surfaces may be used as deicing solutions.


Subject(s)
Fabaceae , Rosa , Surface Properties , Rosa/chemistry , Prospective Studies , Wettability
2.
J Adv Prosthodont ; 16(1): 57-65, 2024 02.
Article in English | MEDLINE | ID: mdl-38455677

ABSTRACT

PURPOSE: The aim of this stuldy was to compare the clinical marginal fit of CAD-CAM inlays obtained from intraoral digital impression or addition silicone impression techniques. MATERIALS AND METHODS: The study included 31 inlays for prosthodontics purposes of 31 patients: 15 based on intraoral digital impressions (DI group); and 16 based on a conventional impression technique (CI group). Inlays included occlusal and a non-occlusal surface. Inlays were milled in ceramic. The inlay-teeth interface was replicated by placing each inlay in its corresponding uncemented clinical preparation and taking interface impressions with silicone material from occlusal and free surfaces. Interface analysis was made using white light confocal microscopy (WLCM) (scanning area: 694 × 510 µm2) from the impression samples. The gap size and the inlay overextension were measured from the microscopy topographies. For analytical purposes (i.e., 95-%-confidence intervals calculations and P-value calculations), the procedure REGRESS in SUDAAN was used to account for clustering (i.e., multiple measurements). For p-value calculation, the log transformation of the dependent variables was used to normalize the distributions. RESULTS: Marginal fit values for occlusal and free surfaces were affected by the type of impression. There were no differences between surfaces (occlusal vs. free). Gap obtained for DI group was 164 ± 84 µm and that for CI group was 209 ± 104 µm, and there were statistical differences between them (p = .041). Mean overextension values were 60 ± 59 µm for DI group and 67 ± 73 µm for CI group, and there were no differences between then (p = .553). CONCLUSION: Digital impression achieved inlays with higher clinical marginal fit and performed better than the conventional silicone materials.

3.
Clin Implant Dent Relat Res ; 26(2): 427-441, 2024 Apr.
Article in English | MEDLINE | ID: mdl-38419213

ABSTRACT

OBJECTIVES: The aims of this study were to design a novel titanium surface coated with a PVA hydrogel matrix and chitosan-based nanoparticles and to investigate the antibiotic release and its ability to inhibit microbial activity. METHODS: Two drug delivery systems were developed and mixed. Chitosan-based nanoparticles (NP) and a polyvinyl alcohol film (PVA). The size, ζ-potential, stability, adhesive properties, and encapsulation profile of NP, as well as the release kinetics of drug delivery systems and their antimicrobial ability of PVA and PVANP films, were studied on Ti surfaces. The systems were loaded with doxycycline, vancomycin, and doxepin hydrochloride. RESULTS: Nanoparticles presented a ζ-potential greater than 30 mV for 45 days and the efficiency drug encapsulation was 26.88% ± 1.51% for doxycycline, 16.09% ± 10.24% for vancomycin and 17.57% ± 11.08% for doxepin. In addition, PVA films were loaded with 125 µg/mL of doxycycline, 125 µg/mL of vancomycin, and 100 µg/mL of doxepin. PVANP-doxycycline achieved the antibacterial effect at 4 h while PVA-doxycycline maintained its effect at 24 h.


Subject(s)
Chitosan , Nanoparticles , Doxycycline/pharmacology , Drug Liberation , Vancomycin/pharmacology , Polyvinyl Alcohol , Titanium , Doxepin , Anti-Bacterial Agents/pharmacology , Hydrogels
4.
HardwareX ; 15: e00447, 2023 Sep.
Article in English | MEDLINE | ID: mdl-37521147

ABSTRACT

The Atomic Force Microscopy is a very versatile technique that allows to characterize surfaces by acquiring topographies with sub-nanometer resolution. This technique often overcomes the problems and capabilities of electron microscopy when characterizing few nanometers thin coatings over solid substrates. They are expensive, in the half million dollar range for standard units, and therefore it is often difficult to upgrade to new units with improved characteristics. One of these improvements, motorization and automation of the measurements is very interesting to sample different parts of a substrate in an unattended way. Here we report a low cost upgrade under 60 $ to a Dimension 3000 AFM based on a control unit using an Arduino Leonardo. It enables to acquire dozens or hundreds of images automatically by mimicking keyboard shortcuts and interfacing the AFM PCI card.

5.
Langmuir ; 39(15): 5469-5476, 2023 Apr 18.
Article in English | MEDLINE | ID: mdl-37016494

ABSTRACT

Galvanized steel surfaces are widely used in industry as a solution to prevent corrosion of steel tools that operate in outdoor or corrosive and oxidative environments. These objects are coated with a zinc protective layer deposited by hot dip galvanization. Turning the surface of galvanized steel tools into superhydrophobic may lead to very useful functionalities, although it may be a difficult task, because the preservation of the thin zinc layer is a claim. We propose herein the use of a bottom-up approach based on sandblasting, followed by sintering of zinc nanoparticles on the galvanized steel substrate, which allowed us to produce a zinc-made hierarchical structure required for superhydrophobicity. These samples acquired a double-scale structure that led to superhydrophobicity when they were later hydrophobized with a thin fluoropolymer layer. We found that sandblasting might be useful but not mandatory, unlike the sintering process, which was essential to reach superhydrophobicity. We found that, under certain experimental conditions, the surfaces showed outstanding water-repellent properties. We observed that the sandblasting on galvanized steel caused more damage than the sintering process. Sintering of low-melting-point metal nanoparticles was revealed as a promising strategy to fabricate functional metallic surfaces.

6.
Behav Sci (Basel) ; 12(7)2022 Jun 22.
Article in English | MEDLINE | ID: mdl-35877271

ABSTRACT

The prevalence of mental health problems during childhood and adolescence is on the rise. There is a growing interest in the examination of personal variables that may function as risk factors and that may be targeted for effective intervention. This study explores the relationships amongst different aspects of psychological inflexibility (one, typically studied, focusing on the individual's responding to unwanted emotions and cognitions, and another, more recently explored, focusing on the individual's responding to desired thoughts and affective states), emotional intelligence, and mental health symptoms. A total of 129 school-going children (mean age: 11.16 years old) completed a battery of instruments comprising the Avoidance and Fusion Questionnaire-Youth (AFQ-Y17), the Experiential Approach Scale (EAS), the Emotional Intelligence Quotient Inventory (EQi-YV), and the Revised Child Anxiety and Depression Scale (RCADS-30). Results showed that both the AFQ-Y17 score and an EAS subscale score (Anxious Clinging) were significant independent predictors of mental health symptoms in general. Emotional intelligence was predictive only for depression, and both the AFQ-Y17 and the Anxious Clinging EAS subscale significantly incremented the predictive power of a hierarchical linear regression model including all three variables. These results underscore the relevance of psychological inflexibility for child/adolescent mental health, and the need to further explore a specific aspect of inflexibility regarding positive emotions and other appetitive private events.

7.
Internet Interv ; 29: 100561, 2022 Sep.
Article in English | MEDLINE | ID: mdl-35855947

ABSTRACT

Introduction: Acceptance and commitment therapy (ACT) is an effective treatment for chronic pain conditions. ACT seeks to produce clinical change by enhancing Psychological Flexibility (PF). This exploratory (feasibility and preliminary effectiveness) study presents a pilot application of an online ACT group intervention for fibromyalgia (FM) with an extensive Experiential Sampling (ES) assessment of outcome and process variables via smartphone. Method: 5-weekly ACT online group sessions were applied to 9 female FM patients. Questionnaire-based assessments of several clinical outcomes and PF processes were conducted pre- and post-intervention, and at 6-month follow-up. Extensive (6 weeks pre- and 6 weeks post-intervention) smartphone-delivered ES was implemented to gather process and outcome data in the patients' usual contexts. Clinically significant change was evaluated both at the group level and individually. Results: This treatment format appears to be feasible and acceptable to participants, with good adoption and completion rates (75 %) and excellent rates of treatment completion and clinical adherence (100 %). Participants showed significant reductions in affective pain, distress and biopsychosocial impact of FM both post-intervention and at 6-month follow-up (as measured with questionnaires), as well as significant improvements in satisfaction with actions and emotional discomfort (as measured through ES). Multilevel regression analyses indicated that PF-related processes assessed through ES had a significant impact on clinical outcomes and predicted the impact of FM at the 6-month follow-up. Conclusions: A brief online group ACT intervention for FM was both feasible and acceptable to participants. Also, there was preliminary evidence of effectiveness in enhancing pain-related PF and producing clinical benefits in FM.

8.
ACS Omega ; 7(24): 20741-20749, 2022 Jun 21.
Article in English | MEDLINE | ID: mdl-35755365

ABSTRACT

Elastomeric surfaces and oil-infused elastic surfaces reveal low ice adhesion, in part because of their deformability. However, these soft surfaces might jeopardize their mechanical durability. In this work, we analyzed the mechanical durability of elastic polydimethylsiloxane (PDMS) surfaces with different balances between elasticity and deicing performances. The durability was studied in terms of shear/tensile ice adhesion strength before and after different wear tests. These tests consisted of abrasion/erosion cycles using standard procedures aimed to reproduce different environmental wearing agents. The main objective is to evaluate if our PDMS surfaces can become long-lasting solutions for ice removal in real conditions. We found that our elastic surfaces show excellent durability. After the wear tests, the ice adhesion strength values remained low or even unaltered. Although the oil-infused PDMS surface was the softest one, it presented considerable durability and excellent low ice adhesion, being a promising solution.

9.
J Colloid Interface Sci ; 608(Pt 1): 792-799, 2022 Feb 15.
Article in English | MEDLINE | ID: mdl-34689111

ABSTRACT

HYPOTHESIS: Ice adhesion to rigid materials is reduced with low energy surfaces of high receding contact angles. However, their adhesion strength values are above the threshold value to be considered as icephobic materials. Surface deformability is a promising route to further reduce ice adhesion. EXPERIMENTS: In this work, we prepared elastomer surfaces with a wide range of elastic moduli and hydrophobicity degree and we measured their ice adhesion strength. Moreover, we also explored the deicing performance of oil-infused elastomeric surfaces. The ice adhesion was characterized by two detachment modes: tensile and shear. FINDINGS: The variety of elastomeric surfaces allowed us to simultaneously analyze the ice adhesion dependence with deformability and contact angle hysteresis. We found that the impact of these properties depends on the detachment mode, being deformability more important in shear mode and hydrophobicity more relevant in tensile mode. In addition, oil infusion further reduces ice adhesion due to the interfacial slippage. From an optimal balance between deformability and hydrophobicity, we were able to identify surfaces with super-low ice adhesion.


Subject(s)
Ice , Hydrophobic and Hydrophilic Interactions , Physical Phenomena , Surface Properties
10.
Article in English | MEDLINE | ID: mdl-34948482

ABSTRACT

Psychological inflexibility is a transdiagnostic dimension associated to psychological distress and poor mental health and quality of life. While multiple instruments have been developed for the assessment of patterns of inflexible responding to aversive private events (e.g., unwanted cognitions and emotions), the Experiential Approach Scale (EAS) is the first instrument specifically designed to assess inflexible responding to appetitive private events (e.g., desired affective states). In this study, we explored the factor structure, internal consistency, and convergent validity of a Spanish adaptation of the EAS with a convenience sample of college students from Spain (n = 206; 79% female). A two-factor solution demonstrated very good fit to the data and was similar to the original two-subscale EAS structure: Anxious Clinging and Experience Prolonging. The scale showed adequate overall (α = 0.85) and subscale (αs: 0.90 and 0.89) internal consistency. Unlike the original instrument, both subscales were uncorrelated. Anxious Clinging correlated positively with experiential avoidance and with measures of negative affect and psychopathology, and negatively with positive affect, subjective happiness, and life satisfaction. In turn, Experience Prolonging correlated negatively with psychopathology and positively with positive affect, subjective happiness, and life satisfaction. Our results point to Anxious Clinging as the only EAS subscale contributing to psychological inflexibility.


Subject(s)
Anxiety , Quality of Life , Emotions , Female , Humans , Male , Psychometrics , Reproducibility of Results , Surveys and Questionnaires
11.
J Eat Disord ; 9(1): 82, 2021 Jul 08.
Article in English | MEDLINE | ID: mdl-34238379

ABSTRACT

BACKGROUND: The discrepancy between actual and ideal body image is considered an index of body dissatisfaction and a risk factor for eating disorders. While discrepancy has been traditionally tested with figural drawing rating scales, in recent times the use of implicit measures has been explored. METHODS: This study employs the Implicit Relational Assessment Procedure (IRAP) to examine actual-ideal body-size discrepancy in a sample of 130 Spanish college students, as well as its utility to predict symptoms of eating disorders and other body-image relevant measures. Participants completed the Contour Drawing Rating Scale (CDRS). The three smallest and the three largest contour drawings of the CDRS were used as target stimuli in two different IRAP tasks: one in combination with the sample phrases "I am" and "I am not" (that assessed implicit actual body image), another in combination with the phrases "I want to be" and "I don't want to be" (that assessed implicit ideal body image). After completing both IRAP tasks, participants completed explicit measures of body-image psychological inflexibility, body dissatisfaction, and symptoms of eating disorders. RESULTS: Results showed a small implicit bias towards thinness. Participants were faster in affirming than denying that they are thin and that they desire to be thin. They were also faster in affirming than denying that they are fat and that they want to be fat, but to a smaller extent than with thinness. Specifically, the implicit desire to be (or not be) fat emerged as an independent predictor of eating disorder symptoms, psychological inflexibility, and body dissatisfaction that significantly increased the predictive power of CDRS scores. CONCLUSIONS: These findings underscore the need for further research on specific body image implicit beliefs towards fatness, both in subclinical and clinical populations, in order to examine whether willingness to accept the idea that one can have a larger body size can be a suitable target for prevention and intervention in eating disorders.


Body dissatisfaction can be thought of as the discrepancy between actual and desired body size. This is typically measured with rating scales depicting a series of body silhouettes of increasing size, from extreme thinness to fatness. Respondents mark the points that match their current body size and the one they would ideally like to be (the more distance between both, the more body dissatisfaction). Like all self-reports, these scales are liable to self-presentation biases. Experimental procedures that require respondents to answer under time pressure (implicit measures) tap into more automatic reactions that are less amenable to deliberate manipulation. This study used one such procedure (the IRAP) to examine how rapidly participants identified themselves (or not) with pictures of underweight or overweight, and how rapidly they expressed a desire to be (or not) like such pictures. Participants did not show a clear discrepancy between their actual and their ideal body size with the IRAP. However, automatic reactions indicative of acceptance/rejection of the idea of becoming fatter, predicted the degree of body image distress as measured with different instruments. Unwillingness to accept this idea was associated with more severe symptoms of disordered eating.

12.
J Contextual Behav Sci ; 19: 42-49, 2021 Jan.
Article in English | MEDLINE | ID: mdl-33520642

ABSTRACT

Spain, one of the European countries most affected by the COVID-19 pandemic, underwent a strict lockdown between March and May 2020. This study examines longitudinally the evolution of both psychological inflexibility and mental health symptoms in a sample of college students from the beginning and throughout the end of the mandated lockdown period. We present the results from 197 participants who responded to an online survey at least at two of three data-collection waves scheduled at the beginning (N = 226), halfway (N = 172), and end (N = 188) of the lockdown. The analyses revealed that psychological inflexibility and symptomatology increased over time, and that inflexibility at the beginning of the lockdown indirectly predicted self-reported symptoms at the end of the lockdown via autoregressive parallel paths that also connected cross-sectionally to reveal that changes in inflexibility were predictive of changes in mental health. These results present a dynamic and robust relationship between psychological inflexibility and mental health symptoms throughout a relatively long and presumably stressful period of time.

13.
J Colloid Interface Sci ; 589: 166-172, 2021 May.
Article in English | MEDLINE | ID: mdl-33460848

ABSTRACT

HYPOTHESIS: Characterization of contact angle hysteresis on soft surfaces is sensitive to the measurement protocol and might present adventitious time-dependencies. Contact line dynamics on solid surfaces is altered by the surface chemistry, surface roughness and/or surface elasticity. We observed a "slow" spontaneous relaxation of static water sessile drops placed on elastic surfaces. This unexpected drop motion reveals unresolved equilibrium configurations that may affect the observed values of contact angle hysteresis. Drop relaxation on deformable surfaces is partially governed by a viscoelastic dissipation located at the contact line. EXPERIMENTS: In this work, we studied the natural relaxation of water drops formed on several smooth PDMS surfaces with different elastic moduli. We monitored in time the contact angle and contact radius of each drop. For varying the initial contact angle, we used the growing-shrinking drop method. FINDINGS: We postulate that the so-called "braking effect", produced by the surface deformability, affects the contact line velocity and in consequence, the contact angle measurements. We conclude that the wetting properties of elastic surfaces should be properly examined with reliable values of contact angle measured after drop relaxation.

14.
J Exp Anal Behav ; 115(1): 204-223, 2021 01.
Article in English | MEDLINE | ID: mdl-33270247

ABSTRACT

A reversal design was employed for the analysis of transfer of fear and avoidance through equivalence classes. Two 5-member equivalence classes (A1-B1-C1-D1-E1 and A2-B2-C2-D2-E2) were established. Then B1 and C1 were paired with shock (CS+) and served as SD s in avoidance training (B2 and C2 were trained as CS-/S∆ s for avoidance). Further avoidance training followed with D1 and E1 (as SD s) and D2 and E2 (as S∆ s), with the first presentation of each of these stimuli serving as the first transfer test. Afterwards, aversive conditioning contingencies were reversed: B2 and D2 were paired with shock and trained as SD s for avoidance, B1 and D1 were presented without shock (CS-/S∆ s). Transfer was tested again with C1, E1, C2 and E2. This reversal was implemented to allow for the within-subject replication of transfer effects upon changes in the function of only a subset of each class's elements. Avoidance (key presses) and conditioned fear (skin conductance and heart rate) were simultaneously measured. Results show a clear transfer effect for avoidance, with between- and within-subject replications. For physiological measures, transfer effects in the first test could only be imputed on the basis of group-based inferential statistical analysis. Evidence for between-subject replication was weaker, with only a limited proportion of participants meeting the individual criterion for transfer.


Subject(s)
Arousal , Conditioning, Classical , Avoidance Learning , Fear , Humans
15.
Front Psychol ; 10: 2102, 2019.
Article in English | MEDLINE | ID: mdl-31620049

ABSTRACT

Research on implicit attitudes to body image has grown substantially in recent years. The extant evidence reveals an implicit weight bias in the general population that has generally been interpreted in terms of anti-fat attitudes. However, research with the Implicit Relational Assessment Procedure (IRAP) shows that this bias appears to be driven by pro-slim rather than anti-fat implicit attitudes. Besides, the only IRAP study of this sort conducted in Spain found no evidence of such implicit weight bias (with similarly positive attitudes to thinness and fatness). Given the existing differences in body dissatisfaction (BD) among diverse cultural contexts, we predicted that discrepancies in findings about implicit weight bias might be related to differences in BD amongst the samples in the different studies. This study explores whether women with extreme scores in BD (High vs. Low) show different patterns of attitudes to female body shape. Spanish female college students with extreme scores in the Body Shape Questionnaire (BSQ: high ≥ 104, percentile 80; low ≤ 52, percentile 20) completed an IRAP with pictures of overweight and underweight women as target stimuli and the words pleasant and unpleasant as labels. Participants also completed explicit ratings to the same stimuli and clinically relevant measures of body image related distress. Results showed an implicit weight bias only for women high in BD. While both groups showed equally positive implicit attitudes to thinness, only women with low BD showed implicit positive attitudes to fatness (and hence no bias). In turn, both groups presented a clear pro-thin/anti-fat explicit bias with positive ratings for underweight pictures and negative ratings for overweight pictures. The latter were stronger for the high BD group. Therefore, between-group differences were mainly driven by differences in attitudes to fatness (both implicit and explicit). Both implicit and explicit attitudes to fatness independently predicted eating disorders symptoms and other clinically relevant measures. These results are discussed in terms of their clinical implications.

16.
J Colloid Interface Sci ; 539: 448-456, 2019 Mar 15.
Article in English | MEDLINE | ID: mdl-30605814

ABSTRACT

HYPOTHESIS: Wettability of solid surfaces is mostly probed with sessile drops rather than bubbles because this method is readily followed out. This recurrent use may lead to a misleading connection of certain phenomena to the hydrophobicity/hydrophilicity of materials. For instance, the Cassie-Baxter regime and the wicking effect are generally associated only to hydrophobic and hydrophilic surfaces, respectively. However, the same phenomenology should be observed when air bubbles (underwater conditions) in contact with solid surfaces are used instead. In particular, one might expect that rough-hydrophilic surfaces become superaerophobic due to the appearance of a hybrid dewetting regime, like the Cassie-Baxter regime described for rough-hydrophobic surfaces. Otherwise, rough-hydrophobic surfaces might become superaerophilic due to air-wicking. EXPERIMENTS: To elucidate this issue, in this work, we analyzed the wettability of surfaces with very different intrinsic contact angle and roughness degree. The analysis was performed with both Sessile Drop and Captive Bubble methods. FINDINGS: Our results with captive bubbles for rough-hydrophilic surfaces revealed phenomena only explained by the occurrence of a transition from the Wenzel regime to an "inverse" Cassie-Baxter regime. In addition, our results with captive bubbles for rough-hydrophobic surfaces showed evidences of air percolation through the interconnected asperities. This effect reminds the wicking effect reproduced on rough-hydrophilic surfaces, responsible for superhydrophilicity.

17.
J Vis Exp ; (138)2018 08 15.
Article in English | MEDLINE | ID: mdl-30175989

ABSTRACT

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film. The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.


Subject(s)
Surface Properties , Freezing , Hydrophobic and Hydrophilic Interactions
18.
J Colloid Interface Sci ; 508: 129-136, 2017 Dec 15.
Article in English | MEDLINE | ID: mdl-28822862

ABSTRACT

The analysis of wetting properties of superhydrophobic surfaces may be a difficult task due to the restless behavior of drops on this type of surfaces and the limitations of goniometry for high contact angles. A method to validate the performance of superhydrophobic surfaces, rather than standard goniometry, is required. In this work, we used bouncing drop dynamics as a useful tool to predict the water repellency of different superhydrophobic surfaces. From bouncing drop experiments conducted over a wide range of superhydrophobic surfaces, we found that those surfaces with a proper roughness degree and homogeneous chemical composition showed higher water-repellency. We also conducted a drop condensation study at saturating conditions aimed to determine whether there is direct correlation between water repellency and condensation delay. We found that the drop condensation process is strongly related to the surface topography, as well as the intrinsic wettability. The condensation is promoted on rough surfaces but it is delayed on intrinsically hydrophobic surfaces. However, the differences found in condensation delay between the superhydrophobic surfaces explored in this study cannot be justified by their chemical homogeneity nor their efficiency as water repellent surfaces, separately.

19.
J Colloid Interface Sci ; 505: 692-702, 2017 Nov 01.
Article in English | MEDLINE | ID: mdl-28658655

ABSTRACT

A successful methodology for obtaining hybrid films which allow thermal triggering and continuous, irreversible, control of their hydrophilicity/hydrophobicity nature was developed. Two types of poly(dimethylsiloxane)-silica (PDMS@SiO2) films were prepared for that purpose: A hydrophilic film in which the thermal treatment causes an irreversible gradual increase of hydrophobicity; and a hydrophobic film that turns more hydrophilic upon thermal treatment. The opposite directionality of the change is dictated by the film substrate, on which the same hybrid is deposited. In both cases the thermal treatment induced a phase separation which caused the change in hydrophobicity. The magnitude of change in hydrophilicity/hydrophobicity is continuously controllable in both types of films by either the temperature or heating time. The films were characterized before and after heating by a variety of methods, including contact angle (CA) measurements with the sessile drop and the tilting plate methods, and by X-ray photoelectron spectroscopy (XPS) analysis. A thorough kinetic study was carried out, following the progress of the changes in the wettability property of the surfaces. The kinetics analyses proved that the changes in the wettability in all cases are due to phase separation processes, the directionality of which is determined by the treatment of the substrate on which the films are deposited. By monitoring the change of wettability (ΔCA) at various temperatures, an Arrhenius plot was obtained from which the activation energy and Arrhenius pre-exponential factor for the phase separation were derived, corroborating the proposed mechanism. To the best of our knowledge, this is the first use of phase separation behavior of a hybrid film in order to apply irreversible, thermally controllable change of surface wettability, tailored to proceed in opposite directions, and the first kinetic study of such a process.

20.
Adv Colloid Interface Sci ; 247: 208-222, 2017 Sep.
Article in English | MEDLINE | ID: mdl-28219622

ABSTRACT

Particles adsorbed at liquid interfaces are commonly used to stabilise water-oil Pickering emulsions and water-air foams. The fundamental understanding of the physics of particles adsorbed at water-air and water-oil interfaces is improving significantly due to novel techniques that enable the measurement of the contact angle of individual particles at a given interface. The case of non-aqueous interfaces and emulsions is less studied in the literature. Non-aqueous liquid-liquid interfaces in which water is replaced by other polar solvents have properties similar to those of water-oil interfaces. Nanocomposites of non-aqueous immiscible polymer blends containing inorganic particles at the interface are of great interest industrially and consequently more work has been devoted to them. By contrast, the behaviour of particles adsorbed at oil-oil interfaces in which both oils are immiscible and of low dielectric constant (ε<3) is scarcely studied. Hydrophobic particles are required to stabilise these oil-oil emulsions due to their irreversible adsorption, high interfacial activity and elastic shell behaviour.

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