Micro-rheology on (polymer-grafted) colloids using optical tweezers

Gutsche, Christof; Elmahdy, Mahdy M.; Kegler, K.; Semenov, Ilya; Stangner, Tim; Otto, Oliver; Ueberschär, Olaf; Keyser, Ulrich F.; Krueger, Michael; Rauscher, Markus; Weeber, Rudolf; Harting, Jens; Kim, Y W; Lobaskin, Vladimir; Netz, Roland R.; Kremer, Friedrich

doi:10.1088/0953-8984/23/18/184114

Cited by 20 publications

(17 citation statements)

References 120 publications

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“…Note that the optical tweezer has been widely applied in the microrheological measurements of soft matters including polymer solutions, colloidal dispersions, gels, and biological materials . However, it has some inherent problems.…”

Section: Active Microrheologymentioning

confidence: 99%

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Liu

2017

Macro Chemistry & Physics

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To overcome these shortcomings of macrorheology, a number of novel microrheological methods have emerged during the last few decades, [2] often involving a small tracking or probing particle (micrometer size) dispersed in a softmatter medium. By tracking the fluctuation due to thermal energy or applying an external force, usually in the form of magnetic force or optical trap, one can measure local mechanical responses. The local disturbance in a micrometer scale avoids reconstruction of local viscoelastic response, an inevitable problem in bulk rheology, especially when the probe particle size is smaller than the characteristic length of a soft matter. Depending on whether the probe is manipulated by an external force instead of a random walk due to thermal fluctuation, microrheometers can be generally characterized as active or passive ones. For an equilibrium system, the fluctuationdissipation theorem (FDT) guarantees that these two methods are equivalent. [3] In this review, we will detail these two classes of microrheometers, including their basic principles and typical setups as well as some recently developed hybrid microrheometers, [4][5][6] often used in characterizing polymer solutions and biological materials. Passive MicrorheologyIn a passive microrheometry method, the fluctuation of probes dispersed in a soft-matter medium is detected and analyzed by calculating the mean-square displacement (MSD) often from their video-based trajectories or scattered light intensities. Since the fluctuation of probes in space is driven by an extremely small thermal energy (k B T), the results from a passive method are always fallen inside the linear range of viscoelasticity. Generally, the elastic modulus is estimated within an upper limit of hundreds of Pa, which means that passive microrheometers are more suitable for measuring "soft" materials with a low viscosity and elasticity. Otherwise, the probes would be trapped without a measurable movement. Even newly developed super-resolution microscopes can provide a sub-nanometer resolution, [7] they are still not widely available methods and have a limited frequency range (up to 100 Hz). Mechanical properties of a soft matter can be obtained from MSD by using the generalized Stokes-Einstein relation (GSER). [8,9] In two extreme cases, (1) the probe is dispersed in a Newtonian viscous fluid and undergoes a Brownian motion with an MSD of 〈Δr 2 (t)〉. The viscosity η is related to the translational diffusion coefficient D as Microrheological TechniquesRheological properties of soft matter like polymer solutions/gels, colloidal dispersions, and biological materials have been extensively studied by macroscopic methods. Recently, a set of microrheometers has emerged as powerful tools to investigate the dynamics and structures of homogeneous or heterogeneous soft matter at the micro-or nanoscale. In this review, these microrheometers, including some novel hybrid microrheometers are summarized and compared.

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Section: Active Microrheologymentioning

confidence: 99%

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Liu

2017

Macro Chemistry & Physics

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“…Also, the flow field created by the large particle drags along some of the surrounding crystal causing the movement of an effectively much larger object. In particular behind the probe the drag is increased, since there the crystal is less jammed [12,13]. The particles forming the crystal have a radius of 1.6µm and are kept on the bottom of the container by gravity.…”

Section: Simulation Techniquementioning

confidence: 99%

Hydrodynamic interactions in active colloidal crystal microrheology

Weeber

Harting

2012

Phys. Rev. E

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In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts on the development of defects, the crystal regeneration as well as on the jamming behavior.

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“…This creates a huge osmotic pressure resulting in a marked stretching of the polyelectrolytes [23,24]. The responsiveness of the SPB towards external stimuli such as the ionic strength and pH allows precise control over the spatial dimensions of the particles and their mutual interaction [25][26][27][28].…”

Section: Hanske Et Almentioning

confidence: 99%

Adsorption of Spherical Polyelectrolyte Brushes: from Interactions to Surface Patterning

Hanske

Erath

Kühr

et al. 2012

Zeitschrift Für Physikalische Chemie

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Adsorption of colloidal particles constitutes an attractive route to tailor the properties of surfaces. However, for efficient material design full control over the particle-substrate interactions is required. We investigate the interaction of spherical polyelectrolyte brushes (SPB) with charged substrates based on adsorption studies and atomic force spectroscopy. The brush layer grafted from the colloidal particles allows a precise adjustment of their adsorption behavior by varying the concentration of added salt. We find a pronounced selectivity between oppositely and like-charged surfaces for ionic strengths up to 10 mM. Near the transition from the osmotic to the salted brush regime at approximately 100 mM attractive secondary interactions become dominant. In this regime SPB adsorb even to like-charged surfaces. To determine the adhesion energy of SPB on charged surfaces directly, we synthesize micrometer-sized SPB. These particles are used in colloidal probe AFM studies. Measurements on oppositely charged surfaces show high forces of adhesion for low ionic strengths that can be attributed to an entropy gain by counterion release. Transferring our observations to charge patterned substrates, we are able to direct the deposition of SPB into two-dimensional arrays. Considering that numerous chemical modifications have been reported for SPB, our studies could open exiting avenues for the production of functional materials with a hierarchical internal organization.

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Micro-rheology on (polymer-grafted) colloids using optical tweezers

Cited by 20 publications

References 120 publications

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Hydrodynamic interactions in active colloidal crystal microrheology

Adsorption of Spherical Polyelectrolyte Brushes: from Interactions to Surface Patterning

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