Interpenetrating polymer networks phase domain size

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

Interpenetrating polymer networks are defined eis a combination of two polymers, each in network form. From a practical point of view, an IPN is comprised of two polymers which cannot be separated chemically, do not dissolve or fiow, and are not bonded together. Like most other multicomponent polymer materials, IPN s usually phase separate due to their very small entropy of mixing. However, the presence of the crosslinks tends to reduce the resulting domain size, hence yielding a unique method of controlling the final morphology. 

If the domain sizes are small, only a veiy broad glass transition of the interpenetrating polymer network ean be observed that stretches across the range between the two polymers. In contrast to this, two distinct glass transitions are found when the domains are larger and the two polymers are better separated. In many cases, the two or more polymers of the interpenetrating network form phases that are continuous on a macroscopic scale. 

Donatelli, A.A., Sperling, L.H. and Thomas, D.A., A semiempirical derivation of phase domain size in interpenetrating polymer networks. J. Appl. Polymer Sci., 1977, 21, 1189-1197. 

A. A. Donatelli, L. H. Sperling, and D. A. Thomas, A Semiempirical Derivation of Phase Domain Size in Interpenetrating Polymer Networks, /. Appl Polym. Sci. 21(5), 1189 (1977). Equations for phase domain size in IPNs and semi-I IPNs. Effect of crosslink density, composition, interfacial tension. 

The field of interpenetrating polymer networks now takes its place parallel to the fields of polymer blends, grafts, and blocks. Indeed, most of these materials are useful because they imdergo some kind of phase separation. Many IPNs seem to work best when the degree of phase separation is only partial or the size of the domains is in the tens of nanometer range. Those IPNs composed of an elastomer and a plastic to make flexible materials seem to be the most imique among these materials. 

Improvement in mechanical properties often accompanies addition of one polymer to another for instance, the tensile strength and modulus of PE are increased by the addition of PP [314], There has also been considerable work in the area of interpenetrating polymer networks [227]. The features of major interest have been multiphase morphologies, including the size, shape, and complexity of the phase within a phase structure. Paul et al. [227] has shown that domains are formed by nuclea-tion and growth mechanisms, and then they are modified by diffusion to lower energy structures. 

The concept of interpenetrating the polymer network was introduced in the early 1960s [108]. The basic idea is the formation of blends with two different independent polymer networks on the nano scale. The non-miscibility between two polymers is the general rule and an important question is to know if the gelation takes place before or after the phase separation, because the timing for these two phenomena will govern the size of each network domain [109,110]. 

In the following, we show in detail the strategies to improve the performance of all-polymer photovoltaic cells, which is directly related to the nanostructures of phase separation in active layer, in four aspects (i) Establish interpenetrating network structure by controlling phase separation, (ii) control the domain size and purify the domains, (iii) adjust the diffused structure at the interface between donor and acceptor, (iv) and construct the relationship between film morphology and device performance. 

The development of effective polymeric photovoltaic cells led to the creation of architectures consisting of phase-separated polymer blends [282-286]. Such systems consist of interpenetrating bicontinuous networks of donor and acceptor phases with domain sizes of 5—50 nm, and provide donor/acceptor heterojunctions distributed throughout the layer thickness (Figure 3.21). 

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