A Near‐Infrared Spectroscopy Study on Thermal Transitions of PMMA and PMMA/SiO₂ Nanocomposites

Abstract

Summary: In this work infrared spectroscopy in the near infrared (NIR) range is used to study the dynamics of polymethylmethacrylate (PMMA) as a pure polymer and when it is modified with silica nanoparticles. Different ways of analyzing FT-NIR spectra were explored taking the temperature as the variable of the systems: i) bands shifts in terms of the first moment of the wavenumber; ii) bands shifts in terms of an absorbance ratio method and iii) absorbance variations in terms of the integrated absorbance. The spectroscopic analysis allowed to study thermal transitions in PMMA and PMMA based nanocomposites. In particular the method based on the use of an absorbance ratio is the most sensible to analyze the thermal transitions. All bands considered could be used to detect thermal transitions reflecting how the vibrations of the groups CH 2 ; CH 3 and C¼O are affected by changes in the free volume of the PMMA. It seems that the PMMA dynamics is more driven by the lateral groups than the backbone of the polymer. The presence of silica nanoparticles, at least when 1% by weight is used, restrains the PMMA motion increasing the relaxation temperatures that can be associated with the glass transitions.

Opposite Effects of SiO2 Nanoparticles on the Local α and Larger-Scale α’ Segmental Relaxation Dynamics of PMMA Nanocomposites

“…The absorption band located around 1736 cm −1 can be observed from the spectra, which is attributed to the vibrations of the carbonyl groups in PMMA. As reported in previous literature, the absorption band will broaden or shift in frequency if the carbonyl groups of polymer form hydrogen bonding with nanoparticles [30]. However, as Figure 2 shows, the position and width of the carbonyl groups’ absorption band shows no obvious change in PMMA/SiO 2 nanocomposites, indicating a weak interaction between silica nanoparticles and PMMA.…”

“…The poly(methyl methacrylate)/silica (PMMA/SiO 2 ) polymer nanocomposites with excellent mechanical properties [25,26] and thermal stability [27] have attracted extensive attention, and their segmental dynamics have been widely investigated by various techniques [28,29,30]. The previous studies show that the addition of silica nanoparticles leads to the broadening of the glass transition process, the increase of T g , and the slowing down of the α relaxation process due to the attractive interaction between silica nanoparticles and PMMA [31,32,33].…”

Accurate Evaluation of Dynamics and Specific Interactions in PLA/TiO2 Nanocomposites

“…More recently, the analysis of FTIR-ATR absorption bands has been used for the study of the changes accompanying interfacial conformations and molecular structure in PMMA-silica nanocomposites [3,7]. Among the different IR ranges, spectra in the middle IR range are easier to interpret since; in general, the assignment of the bands corresponds to normal modes of vibration.…”

Effect of a silica nanofiller on the structure, dynamics and thermostability of LDPE in LDPE/silica nanocomposites

“…The second one, however, is more difficult to ascertain, as it mainly depends on the specic interactions taking place between the particles and the polymer chains, which in turn are connected to the size and aspect ratio of the particles. 8,21,22 A factor of paramount importance in the characterization of this type of materials is the uniform dispersion of the nanoparticles within the polymer to avoid effects derived from the potential aggregation of the particles. Quite oen, even small amounts of the nanoller may produce important consequences on the nal properties of the material.…”

“…20 More recently, the analysis of FTIR-ATR absorption bands has been used to study the changes accompanying interfacial conformations and molecular structure in PMMA-silica nanocomposites. 8,21,22 A factor of paramount importance in the characterization of this type of materials is the uniform dispersion of the nanoparticles within the polymer to avoid effects derived from the potential aggregation of the particles. Thus, different approaches have been described in the literature to achieve a good dispersion of nanoparticles into polymer matrices, such as chemical modication of the surface of the nanoparticles or the polymeric matrices to generate specic functional groups, in situ polymerization, or sol-gel methods to create nanoparticles within the polymer, 23 among other methods.…”