Abstract
Carbon fiber (CF) reinforced polymers (CFRPs) have experienced widespread use in various industries. One of the most important parameters that controls the macroscopic property of CFRPs is the interface between a polymer matrix and CF. There is growing evidence to suggest the formation of a bound polymer layer (BPL), i.e., polymer chains that physically adsorb on a filler surface. However, this interface is always in contact with the thicker part of a polymer matrix, rendering its understanding a difficult task. Therein, we use CF-reinforced isotactic polypropylene (iPP) as a rational CFRP. To characterize the BPL on the CF surface, we extracted it from the CFRP using solvent-rinsing with p-xylene. The physical and thermal properties of the BPL were characterized by differential scanning calorimetry and thermogravimetric analysis, while its microscopic structures and dynamics were probed by small-angle neutron scattering and quasi-elastic neutron scattering (QENS) techniques. Subsequently, we employed atomistic molecular dynamics (MD) simulations to complement the QENS results above the bulk melting temperature and reveal details that were experimentally inaccessible. We observed that the degree of crystallinity of the BPL was quite lower than the bulk, while the melting temperature of the BPL remained the same as the bulks. Within the given length and time scales probed by QENS and MD, we also observed that most of the bound chains were mobile, with the formation of a high-density region (less than 1 nm in thickness) near the CF surface. The segmental dynamics of the bound chains probed by both QENS and MD were also much faster than those of the free chains, possibly due to the presence of a free surface region at the topmost surface of the BPL. Furthermore, the MD results demonstrated that the backbone chains and side groups lie nearly flat on the CF surface, which is the driving force for the flattening process of the iPP BPL to overcome the conformational entropy loss in the total free energy.
| Original language | English |
|---|---|
| Article number | 125584 |
| Journal | Polymer |
| Volume | 265 |
| DOIs | |
| State | Published - Jan 16 2023 |
Funding
Fig. 9d shows the ratio of the density between the side groups and the total (shown in Fig. 5). Hence, the side groups tend to migrate not only to the CF-vacuum interface but also the polymer-CF interface. The former is consistent with previous results [95,96] and possibly due to the decreased steric hindrance between neighboring methyl groups. The latter indicates that both the backbone and side group lie nearly flat on the CF surface (as highlighted in Fig. 9e and f) to increase the number of solid/backbone segment contacts, which is the driving force for the “flattening” process of bound chains to overcome the conformational entropy loss in the total free energy, as revealed for bound chains formed in supported polymer thin films [97–99]. The chain arrangements result in the improvement of segmental packing near the CF surface, as evidenced in Fig. 5. Using the selective labeling approach, the effects of tacticity on the flattening process of PP on solids with different segment-solid interactions are currently in progress. For the backbone and side chains of bound chains located slightly away from the CF surface (at z < 0.6 nm), they appear to show preferred orientations depending on z (Fig. 9c & f). At z > 0.6 nm, however, their orientations become randomized (isotropic) (Fig. 9c).The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tadanori Koga reports financial support was provided by National Science Foundation. Tadanori Koga reports financial support was provided by American Chemical Society. Tadanori Koga reports financial support was provided by Mitsui Chemicals Inc.T. K. and M. E. acknowledge financial support from Mitsui Chemicals Inc. T.K. also acknowledges partial financial supports from National Science Foundation (DMR 2210207). Acknowledgment is also made to the Donors of the American Chemical Society Petroleum Research Fund (ACS-PRF 59064-ND7) for partial support of this research. The computational aspects of this work were performed at the Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy Office of Science User Facility at Oak Ridge National Laboratory. This research also used resources of the Oak Ridge Leadership Computing Facility (OLCF), which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725. The QENS experiments at the Materials and Life Science Experimental Facility of the J-PARC was performed under a user program (Proposal No. 2019B0178 and 2020C0004). The SANS experiments at the QUOKKA beamline of ANSTO was performed under a user program (Proposal No. 7557). The authors acknowledge Kathleen Wood, Jitendra Mata, and Anna Paradowska (ANSTO) for their assistance with the SANS experiments. The authors acknowledge the support of the Functional Polymer Consortium (FPC) and the Quantum Beam Analyses Alliance (QBAA). T. K. and M. E. acknowledge financial support from Mitsui Chemicals Inc. T.K. also acknowledges partial financial supports from National Science Foundation (DMR 2210207 ). Acknowledgment is also made to the Donors of the American Chemical Society Petroleum Research Fund ( ACS-PRF 59064-ND7 ) for partial support of this research. The computational aspects of this work were performed at the Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy Office of Science User Facility at Oak Ridge National Laboratory. This research also used resources of the Oak Ridge Leadership Computing Facility (OLCF), which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725 . The QENS experiments at the Materials and Life Science Experimental Facility of the J-PARC was performed under a user program (Proposal No. 2019B0178 and 2020C0004). The SANS experiments at the QUOKKA beamline of ANSTO was performed under a user program (Proposal No. 7557). The authors acknowledge Kathleen Wood, Jitendra Mata, and Anna Paradowska (ANSTO) for their assistance with the SANS experiments. The authors acknowledge the support of the Functional Polymer Consortium (FPC) and the Quantum Beam Analyses Alliance (QBAA).
| Funders | Funder number |
|---|---|
| CF surface | |
| Center for Nanophase Materials Sciences | |
| Functional Polymer Consortium | |
| Mitsui Chemicals Inc. | |
| Quantum Beam Analyses Alliance | |
| National Science Foundation | DMR 2210207 |
| American Chemical Society | |
| Office of Science | DE-AC05-00OR22725, 2020C0004, 7557, 2019B0178 |
| Oak Ridge National Laboratory | |
| American Chemical Society Petroleum Research Fund | ACS-PRF 59064-ND7 |
Keywords
- Atomistic molecular dynamics simulations
- Bound polymer
- Chain packing
- Interfacial structures and dynamics
- Quasi-elastic neutron scattering