Amirreza Malekzadeh Dirin

There are many works on the interaction of polymers with surfactants. Intermolecular interactions can be hydrophobic or electrostatic. This depends on the ratio of surfactant and polymer and their structure. Without a detailed description of the problem, it is not possible to explain the reasons for the compression or expansion of the composite.

1.Surface Chemistry of Surfactants and Polymers | Lindman Bjorn, Kronberg Bengt

2.B. Lindman, Colloid Polym. Sci., 294, 1687-1703 (2016)

3.Preprint Nuclear quantum effect in aqueous micellar surfactant solutions

I just can answer part of the question according to my practical experience with surfactants (type poly(ethylenegycol)-aliphatic-block-copolymers) with polyolefins like PE and PP. The idea was to produce a hydrophilic surface by mixing in the melt, but the result was negative, along with a clear softening effect (e.g. lower module). The interpretation was that micelle formation of the additive dominated. For other materials and surfactants we need more information for answering your question.

Dear Amirreza Malekzadeh Dirin, Tg is decreased becauae chains interdistance is increased due to the presence of surfactant molecules. This leads to a reduction of the Cohesive Energy Density (CED) responsible for chain mobility. Note that for most intermolecular forces, the energy of interaction is 1/r^6, r being the separation distance of intercting sites. The free volume decreases because it is filled by surfactant molecules which due to their size have both ease of mobility and packing beneath chains. Yes surfactants are used as plasticizers by acting as previously explained (chains separation). My Regards

You seem to be describing a typical antiplasticization behaviour, but the idea that it becomes more rubbery is perplexing. It may depend on the the actual Tg relative to room trmperature.