ABSTRACT
When determining the surface energies of solids the most frequently utilised method is to measure contact angles for particular probe liquids. The measured contact angles (usually measured in air) are then combined with published values of surface- and interfacial tensions of the liquids to give the surface energy of the solid. It is, however, very seldom that sufficient attention is paid to the impurities, to the experimental (e.g. saturated vapour) conditions chosen and to the heterogeneities (chemical and structural) of the solid surface. In this study five typical probe liquids: octane, hexadecane, diiodomethane, alpha-bromonaphthalene and water have been used to establish the dispersion component of the surface energy of the solid and the hydrophobic interaction occurring at the interface of four solids: hydrophobic/hydrophilic SiO2 and hydrophobic/hydrophilic TiO2. Two (solid/liquid) and three (solid/liquid/liquid) component systems were investigated. The results are compared with previously published results when Alkenyl Succinic Anhydride (ASA) was brought into contact with SiO2 under water. The preferential surface vapour pressure and liquid spreading of the one liquid over the solids in the absence and presence of a saturated liquid vapour were evaluated as sources of errors.
ABSTRACT
Subjects with neck problems, such as whiplash injuries, often complain of disturbed equilibrium and, in some instances, provocation of the neck position can elicit such problems. The importance of neck proprioceptors for maintaining balance is gaining increased interest, moreover the function or malfunction of the otoliths may disturb equilibrium in certain head positions. The aim of the study was to create a reference material for postural control and its dependence on head position in healthy subjects and to compare this with a set of patients with known neck problems and associated vertiginous problems. A total of 32 healthy subjects (16 men, 16 women, age range 21-58 years) as well as 10 patients age range 27-62 years (mean 44 years) with neck problems and associated balance problems since a whiplash injury were tested for postural control using the EquiTest dynamic posturographic model. The normal subjects were initially split into four age groups in order to estimate the effects of age on performance. The postural stability was evaluated for dependence of support surface conditions (stable or sway-referenced), visual input (eyes open or closed) and head position (neutral, left rotated, right rotated, extended backwards or flexed forward) using analysis of variance (ANOVA) with Tukey's post hoc test in case of a significant factor effect. As expected, visual cues as well as stable support surface improve postural stability (p < 0.001). Postural stability is statistically different in the head extended backwards condition compared with the other four head positions (p < 0.001 in all cases) in both patients and controls. Eliminating this test condition from the analysis, only a slight (p < 0.05) difference between head forwards and head turned left remained. This pattern of results remained if the normal subjects were only split into two age groups instead of four. Finally, the patient group exhibited significantly lower postural performance than all the groups of normal subjects (p <0.01), but none of the normal groups differed significantly from each other. It is concluded that the postural control system is significantly challenged in the head extended backwards condition in both normal subjects and patients with previous whiplash injury and persistent neck problems. The patient group differed statistically from all groups of normal subjects. This suggests that neck problems impair postural control, and that the head extended position is a more challenging task for the postural system to adapt to. Whether this is due to utricular malpositioning, central integrative functions or cervical proprioceptive afferents is not within the scope of this study to answer.
