Synthesis of Silica Nanoparticles by Sol-Gel: Size-Dependent Properties, Surface Modification, and Applications in Silica-Polymer Nanocomposites—A Review

Table 3

Various types of silica-polymer nanocomposites reported in the literature together with the details on filler sizes, concentrations, and some selected results.

Polymer matrix	Silica size (nm)	Silica content	Major property changes (with increasing filler content)	Reference
Polyurethane	175, 395 and 730	1–10 wt.%	Constant Tg at different particle size and concentrations	[66]
Epoxy (DGEBA)	400	50–70 wt.%	(i) Decreased CTE and increased Tg; (ii) Increased brittleness	[46]
Epoxy (DGEBF)^a	90	1–7 wt.%	(i) Increased fracture toughness; (ii) Larger deformation resistance (up to 3 wt. %)	[67]
Polyimide	20	10–50 wt.%	(i) Increased dielectric constant; (ii) Enhanced thermal stability	[68]
Epoxy (commercial)	25	1–14 vol.%	(i) Decreased Tg and increased Tβ; (ii) Increased microhardness, fracture toughness, and modulus	[65]
Thermoplastic polyurethane	7	10 wt.%	(i) Decreased Tg; (ii) Increased shear and storage modulus; (iii) Increased tensile and peel strength	[69]
Epoxy (DGEBA)^b	240 & 1560	30 vol.%	(i) Increased storage and loss modulus; (ii) Decreased Tg with the increase in the fraction of 1560 nm particles	[70]
Epoxy (commercial)	N/A	10–30 phr	(i) Decreased Tg (up to 20 phr); (ii) Decreased storage modulus and elastic modulus (up to 20 phr)	[71]
Epoxy (DGEBA)	75 and 330	1–5 wt.%	(i) Increased aggregation level; (ii) Increased elastic modulus (modeled); (iii) Higher modulus for smaller particles	[72]
Epoxy (TGDDM)^c	12.5	5 and 10 wt.%	(i) Decreased Tg, constant Tβ; (ii) Increased elastic and yield modulus; (iii) Increased brittle fractureness	[73]
Epoxy (DGEBA)	10–20	10–70 wt.%	(i) Decreased Tg; (ii) Increased thermal stability	[74]
Acrylic polymer^d	15–20	10–50 wt.%	(i) Increased thermal stability; (ii) Enhanced hardness; (iii) Excellent optical transparency	[75]
Epoxy	4000	14–39 vol.%	(i) Increased Young’s modulus; (ii) Immonotonic variation in the yield strength and yield stress	[76]
Epoxy (BPA)^e	9	2.17 vol.%	(i) Decreased frictional coefficient and specific wear rate; (ii) Modified silica nanoparticles promote cure reaction of epoxy	[77]
Polyurethane	14–260	1–4 wt.%	(i) Increased Tg; (ii) Tg increased with particle size up to 66 nm and then decreased; (iii) Decreased surface and interface free energies by incorporation silica	[78]
Polystyrene	25–200	5–10 wt.%	(i) Increased DTA peaks; (ii) Strong interaction between silanes group and polymer chains	[59]
Polyurethane	30	5	Increased SiO2 dispersion	[79]
Polypropylene	50–110	1–5 wt.%	(i) Larger thermal degradation stabilization; (ii) Larger elastic modulus	[85]

^aDiglycidylether of bisphenol F; ^bDiglycidylether of bisphenol A; ^cTetraglycidyl 4-4′-diaminodiphenylmethane; ^dBased on 3-(trimethoxysilyl)propyl methacrylate; ^eBisphenol A epoxy resin (type E-51).