Yongfeng Men profile

Structure formation in polymeric systems, Structure-properties relationships in polymers, Application of small angle scattering technique in polymeric systems.

Current Research

Film formation of polymeric latex dispersion

Polymeric latex dispersions consist of polymeric particles with a diameter of about 100 nm that are dispersed in water. Upon drying, they form void-free films of colloidal face-centered cubic (fcc) structure. Such a process was effectively visualized via synchrotron small angle X-ray scattering (SAXS) technique. Peculiar effects that can only be observed via X-ray technique include shrinkage of individual particles after water evaporation which can be attributed to the collapse of hydrophilic polymers at the surface of particles and the formation of macroscopic fiber symmetric colloidal crystals under directional drying condition.

Deformation mechanism of soft colloidal crystalline latex film

Colloidal crystals made by the soft polymeric particles possess mechanical stability that can be macroscopically deformed. Structural changes at colloidal crystalline lattice constant scale upon stretching were followed by synchrotron SAXS. It was found that the affinity of the microscopic crystalline deformation with respect to the macroscopic one changes with the angle between stretching direction and the normal of the crystallographic (111) plan.

Microscopic structural evolution during tensile deformation of polyethylene

Careful scanning synchrotron SAXS experiments on tensile deformed high density polyethylene revealed new information on the microstructural changes as a function of strain. Transition from spherulite to fibrillar structure was found to start at a strain of 0.4. The original sheared lamellae underwent severe internal deformation so that they were even less stable than the newly developed thinner lamellae.

Selected Publications

1. In situ observation of tensile deformation processes of soft colloidal crystalline latex fibers, Macromolecules, 2009, 42, 4795-4800.

2. GIUSAXS and AFM studies on surface reconstruction of latex thin films during thermal treatment, Langmuir, 2009, 25, 4230-4234.

3. In-situ observation of drying process of a latex droplet by synchrotron small-angle X-ray scattering, Macromolecules, 2008, 41, 5073-5076.

4. Effect of annealing on the deformation mechanism of a styrene/n-butyl acrylate copolymer latex film investigated by synchrotron small-angle X-ray scattering, Macromolecules, 2008, 41, 4353-4357.

5. Facial preparation of macroscopic soft colloidal crystals with fiber symmetry, Langmuir, 2008, 24, 1617-1620.

6. Structural evolution of tensile-deformed high-density polyethylene during annealing: scanning synchrotron small-angle X-ray scattering study, Macromolecules, 2007, 40, 7263-7269.

7. Non-affine structural evolution of soft colloidal crystalline latex films under stretching as observed via synchrotron X-ray scattering, Langmuir, 2006, 22, 8285-8288.

8. Structural changes and chain conformation in cold-drawn polyethylene after annealing by means of small and wide angle X-ray scattering and small angle neutron scattering, Journal of Physical Chemistry B, 2005, 109, 16650-16657.

9. Synchrotron ultra small angle X-ray scattering studies on tensile deformation of poly(1-butene), Macromolecules 2004, 37, 9481-9488.

10. Mechanical a-process in polyethylene, Macromolecules 2003, 36, 4689-4691.

11. Critical strains in poly(e-caprolactone) and blends with poly(vinyl methyl ether) and poly(styrene-co-acrylonitrile), Macromolecules 2003, 36, 1889-1898.

12. Role of the entangled amorphous network in tensile deformation of semi-crystalline polymers, Physical Review Letters 2003, 91, 095502.