Critical Phenomenon During Drying of Semiaromatic, Transparent and Soluble Polyimide Cast Films: Real-Time Observation of Birefringence and Other Integrated Parameters

Abstract

A newly developed real-time multifunctional monitoring system was used to track in-plane and out-of-plane birefringence, weight, thickness and surface temperature of semiaromatic, transparent, and soluble polyimide cast films during drying. At a critical point during drying, out-of-plane birefringence develops rapidly when the cast film undergoes vitrification. The rapid development of out-of-plane birefringence is attributed mainly to polymer chain orientation caused primarily by in-plane confined drying induced by thickness reduction and secondarily by shrinkage stress development in the process of vitrification. Shrinkage stress and its magnitude depend on the details of freezing-in process as dictated by the coating and drying variables. Some drying solutions also found to develop a small negative in-plane birefringence with the higher refractive index in the direction transverse to the air flow direction and it is attributed primarily to the residual stress development. In addition, the influence of solvent type on this phenomenon was studied using series of polar organic solvents.

Real time optical and mechano-optical studies during drying and uniaxial stretching of Polyetherimide films from solution

“…10 shows, high boiling point and/or solubility of solvent NMP yields a lower out-of-plane birefringence. The same phenomenon is also found in an earlier study from our group [42]. Since more NMP solvent is remained at the given drying time, chain relaxation is more favorable which decreases the preferential orientation of polymer chains.…”

“…As the result of a rapid evaporation of solvent near the film's surface and a slow diffusion of solvent molecules from interior to the top surface, a solid skin layer may form that may act as a barrier entrapping the residual solvent away from the surface. Since the drying front develops along the air flow direction traveling from upstream to downstream, the thickness reduces at upstream edge initially and this profile propagates towards the downstream edge [42]. Additionally, there is a slight temperature decrease due to evaporative cooling at the early stage of drying.…”

Kinetics of electric field induced vertical orientation of halloysite nanotubes in photocurable nanocomposites

“…A real time measurement [35][36][37] system was developed to track fast temporal changes of in-and out-of-plane birefringence, thickness and weight during drying of solution cast lms ( Fig. 1(a)).…”

Directed Electric Field Z‐Alignment Kinetics of Anisotropic Nanoparticles for Enhanced Ionic Conductivity

“…Details of the instrument and its measurement capabilities on various polymeric systems can be found elsewhere. [ 56,[58][59][60] For this study, its design was enhanced to measure the changes in both in-plane and out-of-plane birefringence during electric fi eld application. It uses two indium tin oxide (ITO) coated glasses on top of each other separated by a glass spacer which is placed in the light path (Figure 1 b) of the optical system described below.…”