Thank you for your question. First of all, it is important to know that are various chemical treatments such as coupling, grafting, silanation etc in which we use some chemical as agent for the following purpose

1. to increase the compatibility of ceramic with matrix ( which means we Have to increase the interfacial bonding between them because both ceramic and polymer matrix are of opposite polarity so in order to increase interfacial shear strength we use coupling or grafting agents.

2. More good bonding means more strength thereby resulting in enhanced mechanical properties such as tensile strength, flexural strengTh, compressive and impact strength.

For more information read my article about surface treatments

regards

saif

In addition of valuable answer of Saif Wakeel.

It is important take in account termal properties of both matrix (polymer) and ceramic. In general, the thermal conductivity of ceramics is higher than that of a polymer. Therefore, the thermal conductivity of the composite will not be too high. Also important are the coefficients of thermal expansion. As a rule, the polymer has a higher coefficient of expansion. Therefore, when the temperature changes, the matrix should exhibit plastic properties, i.e. the ability to maintain adhesion in the face of internal stresses. With a given composition (i.e., fixed types of polymer matrix and ceramic filler), it is necessary to optimize their proportion. Of course, this optimal ratio will be different for different sizes of ceramic particles. Sometimes it makes sense to use not a single fraction, but two (including fraction with other particle shape, for example needles or fibers) or even more. Those, optimization according to the target applied property leads to the need to research the characteristics of the composition not only when the ratio of the components changes, but also when the particle size distribution characteristics change in the required temperature range, as well as changing this property during thermal cycling.

Fillers or fibers are usually added to a polymer matrix for various reasons:

- to make it cheaper (this is an old approach, but was widely used in PVC compounds or in certain thermosets)

- to confer special, new properties, such as higher strength (reinforcing fillers), higher modulus (mainly fibers), higher heat or electrical conductivity, color (masterbatches), magnetic properties, nonlinear optical properties etc.

Depending on your goal surface treatment may be advantageous or disagvantageous. Ceramics or glass exhibit high surface energy, while polymers usually exhibit low surface energy. This, in principle, would mean strong adhesion provided that the polymer chains can penetrate beween the filler particles. In the case of non-treated particles the filler aprticles tend to agglomerate - sometimes with high energy, so the breakdown of the filler structure is not easy. If you aim e.g. in rubbers is to increase strength, non-treated filler particles give sometimes better results, as the filler agglomerates are non-spherical, while treated particles are smaller, better disperced but result in lower enhancement of the strength. Again, if you want to use conductive particles to increase the conductivity of the composite, better wetting and de-agglomeration may increas the percolation threshold. Therfeore, you should always consider what is your purpose with surfacce treatment.

When selecting the surface treatment agent you should consider the reactivity (surface chemistry) of both filler and polymer matrix. Standard silanes are used with silicates, while titanates with some other ceramic or carbon based fillers, long chain aliphatic acids with carbonates and so on. Chemical bonding between the filler particle and the matrix can be both advantageous and disadvantageous (e.g. with respect to impact strength). So in general it is hard to answer your question buth there are food books and review articles devoted to this topic.