Dr. Weijia Wen 温维佳

Professor

Department of Physics

Hong Kong University of Science and Technology 

Clear Water Bay,  Kowloon 

Hong Kong

 

Tel: (852)-23587979

Fax: (852)-23581652

Email: phwen@ust.hk

 

Professor Wen's main research interests include soft condensed matter physics, electrorheological (ER) and magnetorheological (MR) fluids, field-induced pattern and structure transitions, micro- and nano-fluidic  controlling, microsphere and nanoparticle fabrications, thin film physics, band gap materials, metamaterials and nonlinear optical materials.

  

 Electrorheological (ER) and Magnetorheological (MR) Fluids 
 

ER fluids denote a class of materials consisting of nanometer to micrometer sized dielectric particles dispersed in a liquid, whose rheological properties are controllable by an external electric field. In particular, they can reversibly transform from a liquid to a solid within one hundredth of a second. While in the solid state (with the electric field applied), the strength of that solid, measured by the yield stress, is the critical parameter that governs the application potential of the ER fluids.

  Smart droplet via ER fluid (Soft Matter)

ER fluid and its application in microfluidics (Annual Review: Fluid Mech.)

Universal Logic Gate by ER fluid (Soft Matter)

Single-phase ER Effect (Soft Matter) 

Micro-mechanism of ER Fluid (Phys. Rev. Lett.)

Electrorheological Fluid Dynamics (Phys. Rev. Lett.)

Review Article for ER fluid (Soft matter)

The Giant Electrorheological Effect  (Nature Materials)

The yield stress of nanoparticles-based ER fluid is more than 250 kPa  (Appl. Phys. Lett)

Dielectric Electrorheological Fluids: Theory and Experiment  (Advances in Physics)

Frequency Dependence of the ER Effect and the Role of Water  (Phys. Rev. Lett.)

The Ground State of the MR Fluids  (Phys. Rev. Lett.)

Field-Induced Structural Transition from BCT to FCC in EMR Fluid  (Phys. Rev. Lett.)

 
  Microfluidic Devices; Micro- Nano-fabrications

Microfluidic devices are new generation micro-chips which will be widely used in Bio-microchip, Chemical reaction technology, lab-on-a-chip and other research areas. Our microfluidic devices are mostly associated with ER techniques developed recently in our laboratory. The merits of which are its fast response time, digitalization, easily controlling, and good reliability.

Nanofluidic Mixing (Appl. Phys. Lett)

Single Nucleotide Polymorphism detection (Biomedical Microdevices)

DNA detection in microfluidic chip-based assays (Microchim Acta)

Three-dimensional thermal mapping within microfluidic chip (Scientific Reports)

Micro-reaction with microfluidic chip (Analytical Chemistry) 

Universal logic gate from hybrid divider (Lab on Chip)

Interchangeable Micro-PCR device (Biomedical Microdevices)

Cell Micro-patterning (RSC Advances)

Local Contact Angle on a Heterogeneous Surface (Langmuir)

Logic gate with smart colloid (Lab on a Chip)

Wax-bonding Microfluidic Chips (Lab on a Chip)

"3D microfluidic chips" (Lab on a Chip)

"Smart Window" (Appl. Phys. Lett.)

Smart droplets (Soft Matters)

Core-shell microspheres (Advanced Functional Materials)

PDMS Conducting composite ( Advanced Materials)

Micro thermo-indicator for microfluid  (Appl. Phys. Lett.)

Micro-heater (Appl. Phys. Lett.)

Microfluidic pump (Appl. Phys. Lett.)

Hybrid microfluidic mixer (Phys. Rev. Lett.)

ER fluid-based flexible platform (Appl. Phys. Lett.)

Microspheres and Nanoparticles
  The team in UST initiated the development of techniques to fabricate multiply-coated microspheres with different desired properties. In addition to its utility in ER suspensions, such microspheres also provide a new tool for  basic research in condensed matter physics.

Carbon-doped SiO2 nanoparticles for photocatalysis (Nanoscale)

Honeycomb structural microspheres (Small)

Hollow Titania microspheres (Chem. Comm.)

Multi-core microspheres (Langmuir)

Magnetically responsive microspheres (Appl. Phys. Lett.)

Interaction between two magnetic microspheres (Appl. Phys. Lett.)

The Significant Improvement of ER Fluids in 1997 by Using Multilayer-Coated Microspheres  (Phys. Rev. Lett.)

A Novel Class of Planar Magnetic Colloidal Crystals  (Phys. Rev. Lett.)

               
 
    Functional Materials: Fractal Photonics; Metamaterials
 

A specific class of planar conducting fractals possesses a series of self-similar resonances, leading to multiple gaps and pass bands for electromagnetic waves over an ultra-wide frequency range. The important feature of this material is that it exhibits not only the tunable multiple bands but also subwavelength properties in lateral dimensions, as well as simulates the functions usually exhibited by three-dimensional photonic crystals.

 

 Optical conductivities and signatures of topological insulators (Phys. Rev. B)

Thermal coherence properties of topological insulator (Phys. Rev. B)

Subwavelength polarization rotators (Optics Letters)

Resonant waveguide sensing (Biomedical Optics Express)

Fano Effect --Terahertz extraordinary transmission (Appl. Phys. Lett.)

Resonant terahertz transmissions (Optics Express)

"Fractal THz Antenna" (Appl. Phys. Lett.)

EM wave field rotation effect (Phys. Rev. Lett.)

Resonances-induced transmission (Optics Express)

Acoustic wave transmission through bull's eye structure (Appl. Phys. Lett.)

3D H-fractal and its photonic bandgap properties  (Phys. Rev. B)

Surface resonant-states-enhanced acoustic wave tunneling (Phys. Rev. Lett.)

Acoustic and EM wave Metamaterials (Phys. Rev. B)

Surface electric field determination of hole array (Appl. Phys. Lett.)

Fluid-solid composite (Phys. Rev. Lett.)

Negative refractive index effect for EM wave tunneling (Appl. Phys. Lett.)

Resonant transmission of EM wave through a metal plate (Phys. Rev. B)

Electromagnetic wave tunneling    (Phys. Rev. Lett)     Movie

Metallic planar fractal with photonic band gaps in microwave  (Phys. Rev. Lett.)

 

 

 

 

 

 

 

 
 
   Optical Materials and Thin films
 

Optical materials with large third-order nonlinear susceptibility, χ(3), are essential for light-controlled phase and refractive index modulation for future applications in optical computing, real-time holography, optical correlators and phase-conjugators. The nonlinear composite materials with χ(3) up to ~105esu.

Photoluminescence from Au nanoparticles (J. Opt. Soc. Am. B)

Multilayer gold nanoparticle-doped thin film  (J. Opt. Soc. Am. B)

Optical nonlinearity of nanocrystalline Au/ZnO Composite Films  (Optics Letters)

Preparation and characterization of Au/SiO2 multilayer composite films with nonspherical Au particles (Appl. Phys. A )