Strain‐Based Temperature Memory Effect for Nafion and Its Molecular Origins

Abstract

A shape memory polymer traditionally refers to a polymer that can memorize one temporary shape and recover to its permanent shape upon exposure to an external stimulus. Although this basic concept has been known for at least half a century, recent advances have led to the discoveriy of previously uncovered memory properties that challenge the traditional concept of shape memory polymers. In particular, a temperature memory effect refers to the capability of a polymer to memorize temperatures instead of shapes. Thus far, the reported temperature memory effect has been established under iso‐strain stress recovery conditions, in which the maximum recovery stress appears at a temperature roughly identical to the deformation temperature. This effect can be called recovery stress based temperature memory effect. In this work, experiments were designed in an attempt to establish a temperature memory effect based on the stress free strain recovery behaviors of Nafion. The results show that, under carefully selected conditions, the temperature at which a maximum strain recovery rate is observed can indeed be quantitatively related to the deformation temperature. In addition, indications that the polymer is capable of memorizing more than one deformation temperature (i.e., multi‐temperature memory effect) are shown. The molecular origin of Nafion’s temperature memory effect is elucidated through small angle neutron scattering study.

Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers

“…Figure 3a,b shows that a lower programming temperature has two effects: On the one hand, it results in a faster shape recovery rate. This phenomenon is referred as temperature memory effect of SMPs under free recovery condition 55,57,60 . On the other hand, however, it leads to lower shape fixity, indicating that a large portion of the programmed deformation is recovered right after unloading.…”

“…Previous experimental work revealed complicated dependency of the SM performance on thermo-temporal conditions in an SM cycle. For example, the recovery of SMPs programmed under the same conditions strongly depends on the recovery temperature and heating rate in the recovery step 43,[46][47][48][49][50][51][52] ; in addition, the programming temperature has been shown to affect significantly the free recovery behaviour for SMPs under the same thermo-temporal recovery conditions 31,[53][54][55][56][57] . To date, because the recovery behaviour of an SMP depends on the aforementioned multiple thermo-temporal input parameters, there is no clear understanding how these input parameters can affect the SM performance individually or collectively.…”

Interplay between α-relaxation and morphology transition of perfluorosulfonate ionomer membranes

“…Several applications rely on the understanding of the nature of a-relaxation. The a-relaxation temperature is the underlying parameter to control Nafion shape/temperature memory effects [20], and the PEFC performance at high temperatures [3,5,6]. However, the overriding mechanism of a-relaxation is not fully understood and has imposed a challenge to various research groups for the last 30 years [1e3, 5,7e9].…”

Dicer controls CD8+T-cell activation, migration, and survival

“…A reversible movement could be observed when polymers with crystallizable segments are held under an externally applied constant stress (3,8). Recently temperature-memory polymers (TMPs) enabled the programming of the switching temperature (19,20). Also this temperature-memory effect (TME) is limited to a onetime, one-way effect.…”