Demonstration of a multiscale modeling technique: prediction of the stress–strain responseof light activated shape memory polymers

Abstract

Presented is a multiscale modeling method applied to light activated shape memorypolymers (LASMPs). LASMPs are a new class of shape memory polymer (SMPs) beingdeveloped for adaptive structures applications where a thermal stimulus is undesirable.LASMP developmental emphasis is placed on optical manipulation of Young’s modulus. Amultiscale modeling approach is employed to anticipate the soft and hard statemoduli solely on the basis of a proposed molecular formulation. Employing such amodel shows promise for expediting down-selection of favorable formulations forsynthesis and testing, and subsequently accelerating LASMP development. Anempirical adaptation of the model is also presented which has applications insystem design once a formulation has been identified. The approach employsrotational isomeric state theory to build a molecular scale model of the polymerchain yielding a list of distances between the predicted crosslink locations, orr-values.The r-values are then fitted with Johnson probability density functions and used withBoltzmann statistical mechanics to predict stress as a function of the strain of thephantom polymer network. Empirical adaptation for design adds junction constrainttheory to the modeling process. Junction constraint theory includes the effects ofneighboring chain interactions. Empirical fitting results in numerically accurateYoung’s modulus predictions. The system is modular in nature and thus lends itselfwell to being adapted to other polymer systems and development applications.