## 1 Introduction  
Recently, the development of polymer nanocomposites in the composite industry has grown rapidly because they have superb mechanico-thermal properties and are very promising replacements for conventional polymer composites. Polymer nanocomposites are polymers incorporated with nanometer scale fillers, regardless of the origin of the materials, whether it is inorganic or organic. Synthetic polymers (examples are displayed in Table 1) are frequently utilized for the creation of polymer nanocomposites, including HDPE [1], PP [2], PS [3, 4], DGEBA [5, 6, 7], PEVA [8, 9], PBO [10], SR [11], PAN [12], PUA [13], etc. Synthetic biodegradable polymers (examples are also displayed in Table 1), such as PLA [14, 15, 16, 17, 18], PBAT [19], PBS [20], PVA [21], PCL [22], etc., are also utilized for nanocomposite preparation.  
On the other hand, nanofililers (examples are displayed in Table 2), such as MMT [2; 9; 12; 20], Ag NPs [17; 18], ZnO NPs [15], TiO\({}_{2}\) NRs [3], CNTs [10; 23; 24], CNFs [5; 25; 26], G NPs [11; 13; 23], GO NSs [6; 27], LDHs [22], and HNTs [4], are used in the fabrication of polymer nanocomposites, as they possess a high aspect ratio, large surface area, high stiffness, and low density [17; 20]. The application of bio-based nanofillers, for example, CNCs [15; 18; 28; 29], CNPs [30], NCFs [8; 19], and CNWs [7; 16], also contribute to the production of nanocomposites because they are renewable and sustainable materials.  
Surfactants (examples are also displayed in Table 2), for instance, HTAB [13; 20; 31], DDAB [12; 32], SDS [4; 21], Ultratic PE 105 [19], Niax L-595 [8], HMAC [9], Triton X-100 [6; 10; 11; 24], Beycostat A B09 [15; 17; 18; 28], LAE [29], PEGMONO [14; 16], Pluronic [7; 14], OA [3], AK8805 [5], SA [2], PA [22], Span 60 [30], and BHHB [1], are commonly employed for modifying nanofillers in the preparation of polymer nanocomposites.  
Surfactants have an amphiphilic character, owing to hydrophilic and hydrophobic functional groups [33; 34]. Previous studies have indicated that the surfactants could act as interaction links between hydrophilic and hydrophobic polymers [35; 36; 37]. Furthermore, the presence of surfactants in polymer nanocomposites not only increased the uniformity of the nanofillers dispersion [8], but also improved the compatibility and wettability between polymer and nanofiller [11], as well as enhanced the final properties of the nanocomposites [18].  
\begin{table}
\begin{tabular}{c c c c} \hline
**Nanofiller** & **Abbreviation** & **Surfactant** & **Abbreviation** \\ \hline Montmorillonite & MMT & Hexadecyltrimethylammonium bromide & HTAB \\ Silver nanoparticles & Ag NPs & Didodecyldimethylammonium bromide & DDAB \\ Zinc oxide nanoparticles & ZnO NPs & Sodium dodecyl sulfate & SDS \\ Titanium dioxide nanorods & TiO\({}_{2}\) NRs & Polypropylene glycol ensolvylated and propovylated & Ultratic PE 105 \\ Carbon nanotubes & CNTs & Silicon-based surfactant & Niax L-595 \\ Carbon nanofibers & CNFs & Bis-(2-hydroxyethyl)methylstallow  
In the past few decades, many modification methods have been suggested for the purpose of increasing the mechanico-thermal properties (e.g., tensile strength, flexural strength, impact strength, degradation temperature, glass transition temperature, melting temperature, etc.) of polymer nanocomposites. The non-covalent surface modification method, by utilizing surfactants, is an effective way to modify nanofillers for enhancing the mechanico-thermal properties of polymer nanocomposites. Nonetheless, to the authors' knowledge, no short review has been made covering the work on surfactant-modified inorganic and organic nanofillers for polymer nanocomposites. That is the aim of conducting a systematic review in this paper. This short review is broad, albeit not comprehensive, but is completed with other relevant literatures.