Multilayer method as a tool for depth dependent polymer film photodegradation studies

Abstract

A new polymer film destructive depth profiling protocol is presented for the analysis of photo‐ and thermally degraded thin films on the depth scale of less than 100 microns. The method, demonstrated here on thin films of poly(vinyl chloride) (PVC), provides a means of preparation of thin laminates of high optical quality comprised of many (>20) thin layers of individual thickness less than 15 microns. The constituent layers are fused together under appropriate pressure, temperature and time treatment to yield a film assembly of high optical quality that behaves like a uniform single layer during photodegradation exposure, but which may still be separated after treatment. Compared to previous techniques, this new method is relatively simple and non‐labor intensive. Film adhesive properties are controlled to within ± 5% Concentration depth profiles of polymer photolysis products were reconstructed by analyzing each of the separated layers using UV‐visible spectrophotometry. The continuity of these film assemblies with respect to mechanical properties, adhesive properties and the depth distribution of key photolysis reagents and products was confirmed using photothermal and reference microscopy techniques. Optical absorption depth profiles examined in UV‐ photodegraded poly(vinyl chloride) (PVC) films exhibited the classic dependencies expected in the presence of nitrogen and oxygen atmospheres.

Depth Profiling of the Optical Absorption Coefficient in Ultraviolet-Degraded Poly(Vinylchloride) Films by Dual Beam Light Profile Microscopy

“…The advantage of obtaining a depth profile of the optical absorption coefficient in degraded material is the ease with which such a profile may be calibrated directly in terms of concentration, [4][5][6][7] and ultimately, the % conversion of functionalities in the parent material to the olefinic end product. The present work will demonstrate that the levels of performance available from dual beam LPM depth profiles are comparable to those obtained from a destructive analytical reference technique, 14 and reliably construct a profile of the optical absorption coefficient from polyenes in photo-degraded thin PVC films.…”

“…This classic process in polymer science has been studied by a number of groups using destructive analytical techniques. [2][3][4][5][6][7][8][9]14 Recently, we introduced laser light profile microscopy (LPM) 15,16 as a method for directly observing luminescent and scattering structures in inhomogeneous thin films on a scale of sub-100 m. While a number of methods (as recently reviewed in Ref. 17) have been reported in past works for depth profiling the optical properties of materials, LPM has the distinct advantage of achieving this on a direct basis.…”

Principles of Uv Degradation

“…44 Activation energies calculated from the linear relationships of photodehydrochlorination rate vs. temperature show that the degradation process in nitrogen is slower than in air (E a(nitrogen) =32.1 kJ mol -1 and E a(air) =19.6 kJ mol -1 ). 46 Under an inert atmosphere, the maximum concentration of polyenes is in a 5-10 μm superficial layer of the sample. 46 Under an inert atmosphere, the maximum concentration of polyenes is in a 5-10 μm superficial layer of the sample.…”

“…45 After photodegradation under an oxygen atmosphere, the maximum concentration of polyenes is found at depths of 30-60 μm, with a monotone decrease deeper into the polymer. 46 The propagation of polyenes deeper into the sample is prevented by formation of chromophore centers (polyenes) which screen radiation. 46 The propagation of polyenes deeper into the sample is prevented by formation of chromophore centers (polyenes) which screen radiation.…”

Analytical Methods

“…160,161 The laser mirage effect, a method of photothermal beam deflection, measures heat conduction from the surface of an optically heated sample into an adjacent fluid medium. The nondestructive character of the technique permits long-term studies to be performed on the same sample of slowly evolving processes such as natural weathering.…”