Nanocomposite films have been developed where a galactomannan (guar) matrix was reinforced with cellulose nanowhiskers and plasticized using sorbitol. The properties of these films were compared with films made from guar only. The films were examined using scanning electron microscopy and dynamic vapor sorption. The sorption kinetics properties were analyzed using parallel exponential kinetics (PEK) and this data interpreted using the Kelvin‐Voigt (K‐V) viscoelastic model. Substantial differences in sorption behavior were noted between the guar and cellulose reinforced guar films. Addition of cellulose nanowhiskers (CNWs) to the guar resulted in a change in the shape of the isotherm, as well as a reduced equilibrium moisture content throughout the hygroscopic range. With the guar film, hysteresis between the adsorption and desorption branches of the isotherm occurred up to 75% RH, where it collapsed. Dynamic mechanical analysis showed that the collapse of the hysteresis loop occurred at the glass transition temperature of the guar film. However, addition of CNWs to the guar produced a film where sorption hysteresis was found to occur throughout the hygroscopic range. The applicability of the K‐V interpretation of the sorption kinetics is discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
The emulsification of low molar mass silicone oil (PDMS)-based tamponade agents used in the treatment of complex retinal detachments is a significant clinical problem leading to the patient suffering impairment of vision whilst the tamponade is in place. This is particularly the case in temporal postoperative applications where the tamponade can remain in the ocular cavity for several months. The majority of clinicians prefer to use a PDMS fluid of kinematic viscosity lOOOcS, which offers ease of manual injection. Work is progressing towards the development of tamponades with a reduced tendency to emulsify, through specific tailoring of rheology and interfacial properties.Greater knowledge of the mechanism of intraocular emulsification is being elucidated and has led to the development of 'polymer modified' tamponades with enhanced performance. Such materials are formulated by the addition of a high molecular weight PDMS to the base PDMS fluid. Measurement of the shear viscosity at moderate shear rates is useful in predicting performance during manual injection into the eye. However, the determination of the behaviour in both shear and extension at high strain rates is useful in predicting resistance to intraocular emulsification and in informing future modeling studies. Initial experiments focused on rotational rheometry (shear) and capillary breakup rheometry (CaBER -extension). A range of polymer modified tamponades were characterised -based on PDMS base oils from 100-5000 cS and containing up to 30% by weight PDMS of molecular weight varying in the range 100-800 kDa. Even though the volume occupancy of the polymeric additive ranged from dilute to significantly interpenetrated, a linear response was observed in each case. However, subsequent experiments using capillary rheometry lead to the observation of non-linear behaviour and significant differences in the type of response. Systems with enhanced high strain rate tensile viscosities gave improved performance in in-vitro emulsification tests and are now the subject of clinical trials.The thermodynamic interaction between the polymeric 'solute' and the PDMS fluid 'solvent' was also considered. Interestingly, the PDMS fluids appeared to behave as relatively 'good' solvents, the chains of the polymeric additives being considerably expanded from their unperturbed dimensions.
The second virial coefficient, B(2) is computed of linear rigid rods composed of m equally spaced sites interacting with sites on other rods via the hard-sphere or Weeks-Chandler-Andersen (WCA) pair potentials. The dependence of B(2) on a wide range of separation distance between the sites L and m for both types of potential is computed. Molecular dynamics simulations were carried out of the thermodynamic, static, and percolation properties of the WCA rigid rods in the isotropic phase as a function of rod number density ρ. Simple scaling relationships are discovered between thermodynamic and other static properties as a function of ρ and m, which extend well into the semidilute density range. The percolation threshold distance (PTD) between the centers of mass of the rods complies well with a mean-field random orientation approximation from low density well into the semidilute regime. The corresponding site-site PTD proved more problematic to represent by simple functions, but at high rod density, scales better with the number of sites density rather than the rod number density.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.