Water‐uptake kinetics in poly(methyl methacrylate) films with a fluorescent rotor probe

Abstract

A fluorescence method was adapted to measure moisture-uptake kinetics in films of poly(methyl methacrylate), and data were interpreted in the context of a Fickian diffusion model. The films, 2-60 m thick, were supported on acid-etched microscope slides. They were compared with several freestanding slabs about 1 mm thick. The moisture diffusion in the slabs was Fickian with a diffusivity of 3.2 ϫ 10 Ϫ9 cm 2 /s. The apparent Fickian diffusivity in the films decreased substantially with decreasing film thickness; however, a careful examination revealed that the initial moisture uptake was governed by a thicknessindependent diffusivity for a wide range of film thicknesses.This suggested that the appearance of non-Fickian behavior originated within about a micrometer of the buried interface, possibly as a result of water accumulation beneath the film or slight thickness variations. Moisture uptake in the thickest films was more rapid than in the slabs, most likely because of residual thermal stresses.

Thermal Expansion Behavior of Antiplasticized Polycarbonate

“…Therefore, β -relaxation of an amorphous polymer, i.e., local relaxation mode, is strongly affected by an antiplasticizer, because the mobility in a local mode is suppressed by loss of the free volume. This anomalous but well-known behavior has been reported for various polymers including poly(vinyl chloride), [17][18][19] poly(methyl methacrylate), 15,18,24) and cellulose esters. 18,26,27) PC is also known to show antiplasticization when combined with various materials.…”

“…11) To counter this normal behavior of plasticization, additives known to enhance the modulus are used, which is called antiplasticization. According to previous studies, 3,[15][16][17][18][19][20][21][22][23][24][25][26][27] the decrease in the free volume is believed to be the origin of the modulus enhancement. Therefore, β -relaxation of an amorphous polymer, i.e., local relaxation mode, is strongly affected by an antiplasticizer, because the mobility in a local mode is suppressed by loss of the free volume.…”

Study of Water Adsorption in Poly(N-isopropylacrylamide) Thin Films Using Fluorescence Emission of 3-Hydroxyflavone Probes

“…6,8 Water uptake in a supported polymer film can lead to significant changes in the physicochemical properties of the polymer, which in turn will affect mechanical properties, and this may lead, in medical devices, to such problems as reduced adhesion and mechanical properties, pronounced physical and chemical aging, and swelling and expansion, compromising the intended function of the polymer and also hindering biocompatibility. [32][33][34][35][36] In relatively hydrophilic polymers like pNIPAM, there is always likely to be an appreciable amount of water infiltrating the polymer if it is handled under ambient conditions and precautions are not taken to exclude water infiltration. The situation will be exacerbated when using thin films as the surface area is much larger and this will facilitate water uptake.…”

“…41 However, in the case of fluorophores with a single emission band, there are problems such as photobleaching, excitation source instabilities and variations in probe concentration which can make measurements unreliable, particularly in viscous/rigid polymers. [32][33][34][35] One means of overcoming such problems would be through the use of ratiometric fluorophores. One such class of ratiometric fluorophores are the 3-hydroxyflavones.…”

Fluorescence Analysis of Thermoresponsive Polymers

“…Water uptake in a thin polymer film can lead to significant changes in the physicochemical properties of the polymer [69,70]. In critical applications like medical devices, this may lead to such problems as reduced adhesion and mechanical properties, pronounced physical and chemical aging, and swelling and expansion, compromising the intended function of the polymer and also modulating biocompatibility.…”