Lotus leaf -Traditional, but smart pack from nature- Weon-Sun SHIN DEPT of FOOD & NUTRITION HANYANG UNIVERSITY

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1 Lotus leaf -Traditional, but smart pack from nature- Weon-Sun SHIN DEPT of FOOD & NUTRITION HANYANG UNIVERSITY

2 Learning from nature & tradition Rice culture Buhdism Traditional lunch-box The way of cooking & packing Special functional properties of lotus leaf Surface properties Hydrophilic/hydrophobic in food

3 Lotus

4 Steamed rice in Lotus leaf

Hydrophobicity The standard way to quantify water repellance is to measure the surface tension, the angle between the solid surface and the tangent to the

Hydrophobic refers to angles > 90. Lotus leaf produces superhydrophobic Angles >150. Hydrophilic is from water and love. Water adheres to the surface.

5 Hydrophobicity The standard way to quantify water repellance is to measure the surface tension, the angle between the solid surface and the tangent to the water droplet surface by using a Goniometer. Angles below 40 are considered hydrophilic, and appear to spread on the surface. Hydrophobic refers to angles > 90. Lotus leaf produces superhydrophobic Angles >150. Hydrophilic is from water and love. Water adheres to the surface. Hydrophobic derives from the latin water and fear. Water is repelled from the surface. Superhydrophobic refers to contact angles > 150 degrees. Hydrophilic <40 Hydrophobic >90 Super-Hydrophobic >150

6 Lotus effects Lotus effect is a self-cleaning, waterrepellant property found in some plants. Remarkably, despite constant exposure to dust, dirt, rain and other elements, the leaves of the lotus plant remain clean and dry. This is because the surface of each leaf contains nanometer-sized waxy bumps that prevent dirt and water from adhering. Because the valleys between the bumps are too small for dirt particles to get into, the dirt stays suspended on the tops of the bumps. When a water droplet falls on the leaf, it is also suspended on top of the waxy bumps, creating a lot of surface tension. Beilstein J. Nanotechnol. 2011, 2,

7 Surface tension Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area (J/m 2 ). The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules: A molecule in the bulk liquid experiences cohesive forces with other molecules in all directions. A molecule at the surface of a liquid experiences only net inward cohesive forces.

8 Why meniscus? A. The bottom of concave meniscus (water) B. The top of convex meniscus (mercury)

9 Surface/interface properties Surface/interface tension -Surface pressure- Laplace law* Solution density-dependent: water, ketchup, lecithin-added solution, alcohol, 0.02% SDS solution. <Experiment> Water-/oil-drops, lecithin-added solution, SDS solution & alcohol on either Tefron or filter paper surface Food itself---almost hydrophilic or amphiphilic, but hydropobicity can be increased when finely powered under extremely dry condition <Example> protein has a surface denaturation to form a bubble with a slight shaking & agitating

10 Contact angle(1) Contact angle is measured by producing a drop of pure liquid on a solid surface The angle formed between the solid/liquid interface and the liquid/vapor interface and which has a vertex where the three interfaces meet is referred to as a the contact angle

11 Contact angle(2) The angle between the solid/liquid interface and the liquid/air interface was named as contact angle (θ). The value of the contact angle describes the degree of the liquid wetting the solid surface. The relationship between these parameters is commonly given by the famous Young s equation: cosθ = (γ AS γ WS ) / γ AS (γ AS & γ WS can not be measured, but difference can be derived from the interfacial tensions)

12 Case 1. One contact angle(surface) A : air W : water S : solid Γ : tension γas = γws + γaw cosθ (-1 cosθ 1), that is, cosθ= γas- γws/γaw (γas γws)/γaw = cosθ > 1 : No solution in this equation cosθ = 1 (θ = 0, 180) : Completely wetted solid by liquid (γas γws)/γaw = cosθ < -1 : Strongly hydrophobic material

13 Wettability Wettability defines the degree to which a solid will wet. If a drop spreads out indefinitely and the Contact Angle approaches 0, then total wetting is occurring. In most cases, however, the drop will bead up and only partial wetting (or non-wetting) will occur. The extent to which a solid will wet can be quantified by measuring the Contact Angle.

14 Case 2. Two contact angles(interface) A : air O : oil W : water Spreading pressure can be defined as ΠS = γaw (γao + γow) γaw < γao + γow (ΠS < 0) : droplet will not spread γaw > γao + γow (ΠS > 0) : spreading occur

15 Application <TABLE > Some Interfacial Tensions Material Against Air Against Water Water 72 0 Saturated NaCl solution M SDS in water 41 0 Ethanol 22 0 Paraffin oil Triacylglycerol oil Mercury Paraffin oil ΠS=γAW-(γAO+γOW)=72 (30+50)=-8mN/m -1 (droplet will not spread) Triacylglycerol oil ΠS= γaw-(γao+γow)=72 (35+30)=7mN/m -1 (spreading will occur) can affect the interacion between emulsion droplets & bubbles, Π(spreading pressure) can be altered by surfactants.

16 How to measure? Wilhelmy Plate /Du Noüy ring method: 링을물에잠기게담갔다가위로천천히올리면물이어떤 angle θ 를이루면서곡면을이루게되는데, 이때물표면에 tangential 한방향 (θ 방향 ) 으로힘을받게된다 (A). 계속천천히링을들어올리면물이표면에서떨어지기바로직전얇은 film(b) 을만들게되고, 이때는아래쪽으로만힘이작용한다. 원래링의무게에추가된힘을측정하면결과적으로물의표면장력을구할수있다. (A) (B)

17 아래방향으로힘이작용하고, 또한금속표면의양쪽모두물과닿아있으므로 2 배의장력이걸리는것을생각하면, ΔF=2γcosθ l ΔF max =2γ l(4πr) (cosθ=0, 즉, 1, wetted) ΔF: force measured by module Δf max : max. force just before water fallen 물이떨어지기바로직전의힘 l: distance round the ring γ: tangential force by unit(=surface tension of water) Ring 이액체에서떨어지기직전의힘과링에걸리는힘인기준값의차이, ring 의둘레를알면 surface tension 을계산 ( 기준값 - 바닥에서의평균값 ; 떨어지기직전값 : 급격히힘이떨어지는부분 ) γ =Δf max /2l

18 Reminds Surface hydrophobicity-self-cleaningnoncohesive Surface tension Adhesive properties Contact angle-wettability-spreading pressure Hydrophilic/hydrophobic effects in food system

Surface chemistry. Liquid-gas, solid-gas and solid-liquid surfaces.

Surface chemistry. Liquid-gas, solid-gas and solid-liquid surfaces. Levente Novák & István Bányai, University of Debrecen Dept of Colloid and Environmental Chemistry http://kolloid.unideb.hu/~kolloid/