UCST-Type Thermoresponsive Polymers in Synthetic Lubricating Oil Polyalphaolefin (PAO)

Anchor Group Bottlebrush Polymers as Oil Additive Friction Modifiers

Surface-tethered polymers have been shown to be an efficient lubrication strategy for boundary and mixed lubrication by providing a solvated film between solid surfaces. We have assessed the performance of various graft copolymers as friction modifier additives in oil and revealed important structure-property relationships for this application. The polymers consisted of an oil-soluble, grafted poly(lauryl acrylate) segment and a polar, linear poly(4-acryloylmorpholine) anchor group. Reversible addition-fragmentation chain transfer polymerization was used to access various architectures with control of the grafting density and position of the anchor group. Macrotribological studies displayed promising results with ≈50% reduction in friction coefficient at low polymer treatment rates. QCM-D experiments, neutron reflectometry, small-angle neutron scattering, and atomic force microscopy were used to gather detailed information on these polymers' surface adsorption characteristics, film structure, and solution behavior.

Intrinsic relationship between viscosity, viscosity index, and molecular structure of isoalkanes

CONTEXT

Viscosity and viscosity index are the crucial properties of lubricant base stocks. Molecular dynamics simulation and quantum calculation were used to simulate the five isomers of C₂₆H₅₄ to study the intrinsic relationship between viscosity, viscosity index, and the molecular structure of isoalkanes. The results showed that the intermolecular interaction energy and the volume of rigid-like groups were the intrinsic factors that affected the viscosity and which could describe the viscosity quantitatively. The molecule conformation was studied by calculating the rotational energy barrier of the dihedral angle in the isoalkane molecule, and combined with molecular dynamics, the effect of temperature on the molecular conformation at 313 K and 373 K was further investigated. The α, β, and γ carbon atoms adjacent to the tertiary carbon in the isoalkane molecule were difficult to rotate due to steric hindrance and could be regarded as rigid-like groups at 313 K. The tertiary carbon and the three adjacent carbon atoms formed a regular tetrahedral rigid-like group at 373 K. The changes in the intermolecular interaction energy and the volume of the rigid-like group with temperatures could better describe the viscosity index and reveal the fundamental reasons that affect the viscosity and the viscosity index. The molecular-level understanding of the relationship between the molecular structure and properties of isoalkanes provided theoretical support and scientific guidance for designing isoalkane molecules with specific properties.

METHODS

Molecular dynamics simulation and quantum calculation were performed using Material Studio 8.0 software. The Amorphous Cell module was used to create an amorphous cell. The Foricite module was used for molecular dynamics simulation; the forcefield was assigned as COMPASS II. Nose-Hoover thermostat and Berendsen barostat were applied to maintain the temperature and pressure, respectively. To describe the non-bond interactions, the Ewald method was applied to calculate the van der Waals and electrostatic interactions. The Conformers module was used to study the conformation and the Dmol3 module was used to calculate the conformational energy with fine quality; the functional of GGA-PW91 and the basis set of DNP were used to calculate the energy.

The UCST phase transition of a dextran based copolymer in aqueous media with tunable thermoresponsive behavior

A hydrogen bonded UCST polymer has been developed by grafting of methacrylamide and acrylic acid on dextran via free radical polymerization.

Rheological Study on the Thermoreversible Gelation of Stereo-Controlled Poly(N-Isopropylacrylamide) in an Imidazolium Ionic Liquid

The thermoreversible sol-gel transition for an ionic liquid (IL) solution of isotactic-rich poly (N-isopropylacrylamides) (PNIPAMs) is investigated by rheological technique. The meso-diad content of PNIPAMs ranges between 47% and 79%, and molecular weight (M_n) is ~35,000 and ~70,000 g/mol for two series of samples. PNIPAMs are soluble in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([BMIM][TFSI]) at high temperatures but undergo a gelation with decreasing temperatures. The transition temperature determined from G’-G” crossover increases with isotacticity, consistent with the previous cloud-point result at the same scanning rate, indicating imide groups along the same side of backbones are prone to be aggregated for formation of a gel. The transition point based on Winter-Chambon criterion is on average higher than that of the G’-G” crossover method and is insensitive to tacticity and molecular weight, since it correlates with percolation of globules rather than the further formation of elastic network (G’ > G”). For the first time, the phase diagram composed of both G’-G” crossover points for gelation and cloud points is established in PNIPAM/IL mixtures. For low-M_n PNIPAMs, the crossover-point line intersects the cloud-point line. Hence, from solution to opaque gel, the sample will experience two different transitional phases, either clear gel or opaque sol. A clear gel is formed due to partial phase separation of isotactic segments that could act as junctions of network. However, when the partial phase separation is not faster than the formation of globules, an opaque sol will be formed. For high-M_n PNIPAMs, crossover points are below cloud points at all concentrations, so their gelation only follows the opaque sol route. Such phase diagram is attributed to the poorer solubility of high-M_n polymers for entropic reasons. The phase diagram composed of Winter-Chambon melting points, crossover points for melting, and clear points is similar with the gelation phase diagram, confirming the mechanism above.

Zwitterionic poly(sulfobetaine methacrylate)s in water: from upper critical solution temperature (UCST) to lower critical solution temperature (LCST) with increasing length of one alkyl substituent on the nitrogen atom

Increasing the alkyl length on nitrogen of the polymer changes behaviour from UCST, to soluble, LCST, and insoluble.