A New Probe: AFM Measurements for Random Disorder Systems

Salci, R.; Acar, Damla; Oztirpan, O.; Ramazanoglu, M.

doi:10.1088/0256-307x/36/1/010501

Cited by 2 publications

(6 citation statements)

References 17 publications

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“…Here, ρ is the ratio of the aerosil mass to the total volume of the sample, and ρ s is the aerosil gel density. This parameter is used to define the strength of the disorder effects created by aerosil dispersion in LC [14,[18][19][20]25]. The aerosil nanoparticles were mixed with high purity ethanol.…”

Section: Methodsmentioning

confidence: 99%

“…Aerosil dispersion within LCs not only creates quenched random disorder in the bulk, but also causes topographical changes on the material's surface. For example, increasing aerosil gel density within the sample makes its surface rougher [24,25]. Physical systems where the structural randomness can be controlled, here by varying the aerosil gel density ρ s , also appear in solid state physics.…”

mentioning

confidence: 99%

“…Random pinning of aerosil particles in the bulk changes the surface while they introduce short-range modulations in the nematic and smectic phases in the bulk structure [24,25]. Therefore the randomness in the bulk reflects itself as a self-affine, fractal surface on the boundary.…”

mentioning

confidence: 99%

“…Since aerosil nanoparticles disrupt the ordered state of LCs, the strength of quenched random disorder in the bulk of 8CB LCs can be controlled by adjusting the aerosil gel density ρ s . This parameter has also been used to characterize the LC+aerosil gel samples [11][12][13][14][15][16][17][18][19][20][21][22]25].…”

mentioning

confidence: 99%

“…We scanned the surfaces of our samples with an atomic force microscope (AFM) and obtained surface height profiles with nanometer precision into 256×256 matrices [25]. From the surface data, we first compute the surface fractal dimension D F of each sample and then investigate if D F 's are correlated with ρ s 's, which are known for each sample.…”

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Bulk-boundary correspondence in soft matter

2019

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Bulk-boundary correspondence is the emergence of features at the boundary of a material that are dependent on and yet distinct from the properties of the bulk of the material. The diverse applications of this idea in topological insulators as well as high energy physics prove its universality. However, whether a form of bulk-boundary correspondence holds also in soft matter such as gels, polymers, lipids and other biomaterials is thus far unknown. Aerosil-dispersed liquid crystal gels (LC+aerosil) provide a good testing ground to explore the relation between the controlled variations of the aerosil density within the liquid crystal host bulk and the surface topography of the sample.Here we report on one of the earliest if not the first direct observation of such a correspondence where the controlled strength of random disorder created by aerosil dispersion in the bulk liquid crystal is correlated with the fractal dimension of the surface. We obtained the surface topography of our gel samples with different quenched random disorder strengths by using atomic force microscope techniques, and computed the fractal dimension for each sample. We found that an increase of the aerosil gel density in the bulk corresponds to an increase in the fractal dimension at the surface. From our results emerges a new method to acquire the bulk properties of soft matter such as density, randomness and phase merely from the fractal dimension of the surface.The connection between a material's bulk and its boundary has been one of the guiding principles in several branches of physics in the last decade. The main idea is that the boundary of the system would feature excitations that do not occur in the bulk, yet the physics on the boundary is still determined by the properties of the bulk. For example in topological insulators, the index theorem relates the Chern number quantifying the topology of the insulating bulk to the spectrum of the edge states at the boundary [1][2][3][4]. The holographic principle in high energy physics, also known as gauge/gravity duality, is another example of the bulk-boundary correspondence where the spectrum of the strongly interacting gauge theory in four spacetime dimensions is connected to the weakly interacting theory on the three dimensional boundary via duality [5,6].Here we report on the first ever test of whether bulkboundary correspondence holds in soft condensed matter systems [7,8], particularly in aerosil dispersed liquid crystals ( Fig. 1a). We prepared liquid crystal+aerosil (LC+aerosil) gel mixtures with varying amount of aerosil within, and observed that the aerosil gel density ρ s = m SiO2 /V LC in the bulk is correlated with the fractal dimension of the surface. This experimental verification of the bulk-boundary correspondence in soft matter is the main goal of this study.Liquid crystals (LCs) are not only utilized in screens and TVs, but also used to study phase transitions [9]. Since they possess a rich spectrum of different phases with different types of phase transitions, they stand ou...

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Section: Methodsmentioning

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Bulk-boundary correspondence in soft matter

2019

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Geometric and chemical nonuniformity may induce the stability of more than one wetting state in the same hydrophobic surface

Lazzari

Brito

2019

Phys. Rev. E

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It is well established that roughness and chemistry play a crucial role in the wetting properties of a substrate. Yet, few studies have analyzed systematically the effect of the non-uniformity in the distribution of texture and surface tension of substrates on its wetting properties. In this work we investigate this issue theoretically and numerically. We propose a continuous model that takes into account the total energy required to create interfaces of a droplet in two possible wetting states: Cassie-Baxter (CB) with air pockets trapped underneath the droplet; and the other characterized by the homogeneous wetting of the surface, called the Wenzel (W) state. To introduce geometrical non-regularity we suppose that pillar heights and pillar distances are Gaussian distributed instead of having a constant value. Similarly, we suppose a heterogeneous distribution of Young's angle on the surface to take into account the chemical non-uniformity. This allows to vary the "amount" of disorder by changing the variance of the distribution. We first solve this model analytically and then we also propose a numerical version of it, which can be applied to study any type of disorder. In both versions, we employ the same physical idea: the energies of both states are minimized to predict the thermodynamic wetting state of the droplet for a given volume and surface texture. We find that the main effect of disorder is to induce the stability of both wetting states on the same substrate. In terms of the influence of the disorder on the contact angle of the droplet, we find that it is negligible for the chemical disorder and for pillar-distance disorder. However, in the case of pillar-height disorder, it is observed that the average contact angle of the droplet increases with the amount of disorder. We end the paper investigating how the region of stability of both wetting states behaves when the droplet volume changes.

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A New Probe: AFM Measurements for Random Disorder Systems

Cited by 2 publications

References 17 publications

Bulk-boundary correspondence in soft matter

Bulk-boundary correspondence in soft matter

Geometric and chemical nonuniformity may induce the stability of more than one wetting state in the same hydrophobic surface

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