ABSTRACT
Viscoelastic properties of soft substrates play a crucial role in the evaporation dynamics of sessile drops. Recent studies have revealed that the modification of the viscoelastic properties of substrates changes the dynamics of the three-phase contact line, consequently affecting the evaporation behavior of sessile drops. Notably, these modifications occur without any noticeable changes to the substrate's wetting characteristics or surface topography. However, the individual role of storage (G') and loss (Gâ³) moduli of substrates on drop evaporation dynamics remains unexplored. In this study, we investigate the evaporation dynamics of water drops on two groups of poly(dimethylsiloxane)-based viscoelastic substrates possessing either identical G' with varying Gâ³ or identical Gâ³ with varying G'. Our study reveals that on a substrate with constant shear modulus (G'), a reduction of an order of magnitude in loss modulus shifts the evaporation process from the constant contact radius mode to the constant contact angle mode. We hypothesize that this observed shift in behavior stems from the varying viscoelastic dissipation influenced by the plateau modulus and characteristic relaxation time of polymer gels. Our hypothesis is further supported from the observation that the evaporation process persists on the substrate with constant loss modulus (Gâ³). Our study advances the current understanding of drop evaporation on soft substrates that may find potential applications involving soft composites, biological entities, tissue engineering, and wearable electronics.
ABSTRACT
HYPOTHESIS: A liquid droplet on a rigid polydimethylsiloxane (PDMS) substrate exhibits a higher receding contact angle (θr), therefore, recedes earlier than its softer counterpart. The three-phase contact line of a suspension droplet on a composite rigid-soft PDMS substrate can be selectively tuned wherein the contact line recedes on the rigid substrate sooner and approaches toward the softer side, with microparticles eventually being deposited in the softer substrate region. EXPERIMENTS: A composite PDMS substrate containing soft cores of various shapes (circular and non-circular) surrounded by rigid matrices was fabricated by employing 3D printing and soft lithography. A sessile suspension droplet containing spherical microparticles was deposited on the composite substrate and evaporated under ambient conditions. The evaporation dynamics was recorded and analyzed. FINDINGS: Evaporation-induced patterning (in circular, triangular, and rectangular areas) with sizes ranging from microns to millimetres were obtained. For the first time, by varying the ratio of the rigid-soft regions in the PDMS substrate, we were able to obtain different deposition sizes and shapes from an identical droplet. Instead of using lithographically patterned substrate, our simple methodology by using 3D printing and soft lithography opened up a new avenue for patterning microparticles based on a rigid-soft composite substrate.
Subject(s)
Printing , Physical Phenomena , Printing/methodsABSTRACT
The objective of this study was to measure the maximum superior and inferior lengths of the suprascapular notch with the help of a Vernier caliper and to classify the notches accordingly into four types. This is an observational study, conducted from January to December 2009 at Islamic International Medical College, Rawalpindi. Two hundred and fifty dried human scapulae were procured and measured irrespective of age, gender, race, and sidedness. The maximum superior and inferior lengths were calculated with the help of Vernier caliper. The percentage of notches with greater maximum superior length as compared to inferior length was the highest i.e. 68% (type-III); percentage of notches with equal superior and inferior length was 14% (type-II) absence of notch was noted in 10% of scapulae (type-I) and notches with greater maximum superior length as compared to inferior length was 8% (type-IV). Suprascapular nerve entrapment may be associated with a specific type of suprascapular notch.
