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ISO 즉 International Standard Organization 은 모든 분야의 표준 (Standard) 을 정하는 세계 기관으로서 한국의 표준과학연구원에 해당하는 세계 기관입니다.
Accelerated Centrifugal Force 를 이용하여 Dispersed Material 의 Transmission Profiles 을 측정하여 Dispersion Stability 를 분석하는 기술은 ISO 13097 Guideline 에 정식 등록되어 있는 Technology 입니다.
* ISO 13097 Guideline 표지
이 Guideline 을 정하기 위해 전세계에서 가장 권위있는 전문가들인 ISO 위원 약 30여명이 모여 회의를 거듭한 결과 단 한명의 반대도 없이 전원 찬성하에 Guideline 이 채택되었습니다. 이 회의에 참가한 ISO 위원이 속한 대표적인 기관은 다음과 같습니다.
* DuPont, USA
* Technical Univ. Dresden
* Formulaction, France
* LUM, Germany
* Dispersion Technology Inc., USA
* NIST, USA
* AIST, Japan
* TS-Consulting, Japan
* Micromeretics , USA
* BCS and Malvern, UK
* 기타
ISO/TR 13097 Guidelines 는 다음과 같은 항목으로 구성되어있습니다.
Introduction
1.Scope
2.Terms and definitions
3.Basics of stability
4.Characterizing the change of the state of a dispersion
4.1General comments
4.2Direct methods
4.3.Correlative methods
4.4Procedures to accelerate evaluation of long-term stability
5.Terms and definitions
2. Terms and definitions 에는 다음과 같은 용어들에 대한 정의가 나와 있습니다.
2.1. Agglomeration. Assembly of particles in a dispersed system into loosely coherent structures that are held together by weak physical interactions
2.2. Aggregation Assembly of particles into rigidly joined process
2.3. Coalescence Disappearance of the boundary between two particles (usually droplets or bubbles) in contact, or between one of these and a bulk phase followed by changes of shape leading to a reduction of the toal surface area
2.4. Creaming Rise of the dispersed phase in an emulsion due to the lower density of the dispersed phase (droplets) compared to the continous phase
2.5. Dispersion In general, microscopic multi-phase system in which discontinuities of any state (solid, liquid or gas : discontinous phase) are dispersed in a continuous phase of a different composition or state
2.6. Dispersion Stability Ability to resist change or variation in the initial properties(state) of a dispersion over time, in other words, the quality of a dispersion in being free from alterations over a given time scale
2.7. Flocculation Assembly of particles in a dispersed system into loosely coherent structures that are held together by weak physical interactions
2.8. Flotation Migration of a dispersed solid phase to the top of a liquid continuous phase, when the effective particle density is lower relative to the continuous phase density
2.9. Particle Minute piece of matter with defined physical boundaries
2.10. Ostwald ripening Dissolution of small particles and the redeposition of the dissolved species on the surfaces of larger particles
2.11. Phase inversion Assembly of particles into rigidly joined process
2.12. Phase separation Process by which a macroscopically homogeneous suspension, emulsion or foam separates into two or more new phases
2.13. Sedimentation Settling(separation) of the dispersed phase due to the higher density of the dispersed particles compared to the continuous phase. The accumulation of the dispersed phase at the bottom of the container is evidence that sedimentation has taken place
2.14. Shelf life Recommended time period during which a product(dispersion) can be stored, throughout which the defined quality of a specified property of the product remains acceptable under expected(or specified) conditions of distribution, storage, display and usage
3. Basics of stability
3.1 Stability - Summary
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In order to meet the predefined stability criteria of very stable products, analytical techniques having high resolution/sensitivity need to be used and procedures can be required in order to accelerate the alteration. However, because of the interrelated physical, physico-chemical and chemical properties of a liquid dispsersion, adequate acceleration methos should be chosen and validated in the context of a specific product. (stable product 의 predefined stability criteria 를 충족시키기 위해서는 alteration 을 acceleration 할 수 있는 high resolution/sensitivity 를 가진 분석기법이 필요하고 그 procedures 가 필요하다. 그러나 liquid dispersion 과 관련있는 물리, 물리화학적 그리고 화학적 특성때문에 적절한 acceleration 방법이 선택되어져야 한다.)
3.2 Characteristic features with regard to dispersion stability
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The state of dispersion stability depends upon numerous interrelated physical, physico-chemical and chemical parameters, and its natural is therefore complex. The parameters may be categorized as follows (dispersion 의 stability 상태는 수많은 물리, 물리화학적 그리고 화학적 요인들에 의해 결정되며 그 parameter 들은 다음과 같다. )
a) volume or mass concentration of dispersed phase (e.g. spatial homogeneity, diluted or concentrated)
b) state of the continous phase (e.g. density, viscosity, surface tension, chemical potential, quality of solvent);
c) state of the dispersed phase (e.g. size, shape and density distribution, as well as viscosity of droplets, deformability of particles, structures of particulate surface)
d) interaction between particles/droplets (e.g. electronic and van der waals force, steric and depletion force)
e) interaction betweendispersed and continous phase (e.g. wettability, interfacial tensions, surface and volume rheology, solubility, dissolvability, network formation)
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Two essential aspects with regard to dispersion stability are particle-particle interactions and interactions between the dispersed and continous phase (dispersion stability 관련 두가지 중요한 것은 particle-particle interactions 과 dispersed and continous phase 사이의 interactions 이다.)
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3.3 Alteration of the state of a dispersion
A. creaming, floatationD. flocculation
B. sedimentationE. oswald ripening
C. cCoalescenceF. phase inversion
4 Characterizing the change of the state of a dispersion
4.1 General comments
4.2 Direct methods
4.2.1 Visual observation
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The dispersion is placed in a test-tube, a test-bottle or into the container in which the product is delivered to the end-user and placed into storage. Alterations are visually obervered at appropriate time intervals of days ,weeks or months.Qualitative results are reported as 'yes/no' alterations or 'more/less' than a preset threshold or reference sample. (분산한 물질을 test tube 등에 넣고 저장하는 장소에 위치시킨다. dispersion 의 상태변화를 몇일, 몇주 또는 몇개월의 간격으로 관찰한다. 분산물질의 정성적인 변화 결과는 '예/아니오' 또는 어떤 기준에 대해 '증/감' 으로서 나타내게 된다.)
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4.2.2 Instrumental methods
a) Optical measuring principls
are designed to monitor the changes of the state of dispersion by recording transmission and/or back scattering intensities. (광학적 측정방식은 transmission and/or back scattering 을 측정하여 분산물질의 상태 변화를 확인하도록 설계되어있다.)
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If near-infrared sources are used, in most cases measured intensities do not depend on the optical properties (absorbance) of the continous or dispersed phase. Instruments are available using transmission and/or backscattering (NIR 즉 근적외선을 사용하게 되면 대부분의 경우 측정되어지는 Tranmission 또는 Backscattering 의 양은 continous or dispersed phase. 의 광학적 특성 (흡광도) 에 영향을 받지 않는다.)
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b) X-ray transmission methods
c) Acoustic and electroacoustic spectroscopies
d) Measurements of electrical properties
Direct methods operate in real time and require minutes to months to identify nascent destabilization phenomena. Nevertheless, sensitivity and accuracy of instruments provides the capacity to detect alterations in the state of samples far earlier than visual observations. The techniques described above do not require any sample preparation to measure the kinetics of dispersion state alterations. These methods can be used for measureing shelf life. (direct methods 는 실시간으로 측정하며 destabilization phenomena 를 확인하는데 수분에서 수개월이 필요하다. 그럼에도 측정장비는 visual observation 방법보다 훨씬 더 빨리 sensitivity 와 accuracy 가 탁월한 결과를 나타낸다. 위 기법들은 dispersion 상태 변화를 측정하기위한 별도의 sample preparation 과정을 필요로 하지 않는다. 이 기법들은 물질의 Shelf Life 를 측정하는데 사용될 수 있다.
4.3 Correlative methods
Correlative methods focus on determination of a single physical parameter of the state of a dispersion that is known to correlate with stability of the dispersion. For example one of the following parameters may be measured and compared with pre-defined acceptable values. (correlative methods 는 분산물질의 안정성과 상호연관이 있다고 알려진 dispersion stability 의 하나의 물리적 parameter 를 측정하는 것이다. 예를 들면 다음과 같은 parameter 들중 하나를 측정하고 미리 설정된 기준과 비교하는 것이다.
a) density differences.
b) mean particle size
c) particle size distribution
d) electrophoretic mobility, zeta potential
e) concentration of particles/droplets larger than a stated size value; f) rhelogical parameters
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The advantage of this approach is that the evaluation may be performed immediately after the formulation of a new dispersion or after processing the product. A representative sample is needed, and the measurement technique may sample preparation which can alter the state of dispersion. Care should be taken validate such procedures. (이러한 기법들은 dispersion 을 한 직후 또는 공정을 마친 후 즉시 분산 물질을 분석할 수 있다는 장점이 있다. 그러나 이 방법은 표준적인 sample 이 필요하고 또한 측정을 하기 위한 별도의 sample 준비과정이 필요한데 이 sample preparation 과정에서 분산 물질의 diseprsion state 가 변화될 가능성이 있으므로 많은 주의가 요구된다.)
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4.4 Procedures to accelerate the evaluation of long-term stability
4.4.1 Purpose
Shorter evaluation time in research and develoment (R&D) and pre-shipping quality control (QC) is a challenge for highly stable dispersions (e.g. cosmetics, dispersions for constructionm agrochemicals). (안정성이 매우 뛰어난 분산물질인 화장품, 농약품 등의 분야에서는 R&D 와 QC 에서 분산 안정성의 신속한 evaluation 에 대한 필요가 매우 크다.)
4.4.2 Mechanical procedures
a) Inclination principle
sedimentation and creaming are driven by gravity and their velocities depend on the friction between the separating dispersed and continous phase inopposite directions. Counterintuitively, a phase separation may be accelerated by the fact that particles sediment or cream in an inlined measuring cell faster than if the tube is vertical (Boycott effect). (sedimentation 과 creaming 은 중력에 의해 유도되어 지며 그 속도는 반대 방향으로 작용하는 dispersed phase 와 continous phase 사이의 마찰에 의해 결정된다. 이상하게도 tube 가 직각으로 있을때보다 기울어져 있을때 내용물의 sedimentation or creaming 이 훨씬 더 (2~20배) 빨리 일어난다. (보이콧효과) )
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b) Mechanical energy
1) Centrifugation
is known that centrifugation accelerates phase separation and therefore new or optimized formulations of a given dispersion type may be ranked acording to their stability. The same is true for process optimization or QC of dispersionproduct. As ranking of monitored alterations of the chosen stability metrics at the same measuring conditions, mainly acceleration, is often sufficient, extrapolation to gravity condition would be of interest. Earth acceleration (gravity) g in Stokes law has to be replaced by centrifugal acceleration a. The later depends on the square of the rotational speed and on the distance between the rotor centre and position of the sample region under consideration. The ratio of the centrifugal to gravitational acceleration gives the dimensionless relative centrifugal acceleration (RCA). The RCA-value indicates how much faster the terminal sedimentation or creaming velocity of the particles is in a centrifugal field, compared to gravity under otherwise identical conditions. In other words, centrifugation time multiplied by RCA estimates the appropriate time scale to detect the same changes of dispersion state under gravity..
(centrifugation 은 분산물질의 phase deparation 을 가속화시켜 분산 물질의 stability 정도에 따른 순위를 정하는 것을 가능하게 한다. 주로 acceleration 과 같은 동일한 측정 조건하에서 stability 의 변화를 측정하여 순위를 정하는 것이 충분히 가능하기 때문에 자연 중력 조건에 대한 추정도 가능해진다. Stokes 법칙의 중력값은 centrifugal acceleration 값 a 로 치환 되어지고 이 a 값은 회전속도의 제곱, 그리고 측정범위내의 거리에 비례한다. 중력값에 대한 원심력의 비율이 relative centrifugal acceleration (RCA) 가 된다. 이 RCA 값은 입자가 중력에 비해 원심력하에서 얼마나 더 빨리 sedimentaion 과 creaming 이 일어나는 지를 나타낸다. RCA 와 시간을 곱한 값은 중력하에서 같은 정도의 dispersion state 가 일어나는데 얼마나 걸리는 지를 측정할 수 있게 한다.)
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2) Mixing, vibration and agitation
4.4.3 Thermal procedures
4.4.4 Physico-chemical procedures
5 Prediction of the shelf life of a dispersion
5.1 General comments
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Strictly speaking, shelf life is not only related to the storage time (shelf time), but covers the total life span, from the production, storage, distribution, to the end of usage period with the end-user. (엄격히 이야기하면 shelf life 는 저장기간을 이야기하는 것이 아니라 생산에서 부터 마지막 사용자에 의해 사용되어지기 까지의 전체 life span 을 의미한다. )
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5.2 Comparative analysis
5.3 Predictive analysis
.An important purpose of dispersion stability testing is to establish product shelf life for recommended storage, display and usage conditions. (분산 안정성 testing 의 중요한 목적은 제품의 저장과 사용조건을 위한 shelf life 를 설정하는 것이다. )
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